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feat: add solutions to lc problem: No.1814
No.1814.Count Nice Pairs in an Array
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‎solution/1800-1899/1814.Count Nice Pairs in an Array/README.md

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<!-- 这里可写通用的实现逻辑 -->
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**方法一：式子变换 + 哈希表**
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对于下标对 $(i, j)$，如果满足条件，那么有 $nums[i] + rev(nums[j]) = nums[j] + rev(nums[i])$，即 $nums[i] - rev(nums[i]) = nums[j] - rev(nums[j])$。移项后，有 $nums[i] - nums[j] = rev(nums[j]) - rev(nums[i])$。因此，我们可以将 $nums[i] - rev(nums[i])$ 作为哈希表的键，$nums[i] - nums[j]$ 作为哈希表的值，统计每个键出现的次数，然后计算每个键对应的值的组合数，最后将所有组合数相加即可。
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时间复杂度 $O(n \times \log M)$，其中 $n$ 和 $M$ 分别是数组 `nums` 的长度和数组 `nums` 中的最大值。空间复杂度 $O(n)$。
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<!-- tabs:start -->
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### **Python3**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```python
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class Solution:
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def countNicePairs(self, nums: List[int]) -> int:
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def rev(x):
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y = 0
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while x:
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y = y * 10 + x % 10
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x //= 10
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return y
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cnt = Counter(x - rev(x) for x in nums)
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ans = 0
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mod = 10**9 + 7
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for v in cnt.values():
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ans = (ans + v * (v - 1) // 2) % mod
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return ans
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```
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### **Java**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```java
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class Solution {
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private static final int MOD = (int) 1e9 + 7;
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public int countNicePairs(int[] nums) {
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Map<Integer, Integer> cnt = new HashMap<>();
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for (int x : nums) {
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int y = x - rev(x);
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cnt.put(y, cnt.getOrDefault(y, 0) + 1);
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}
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long ans = 0;
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for (int v : cnt.values()) {
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ans = (ans + (long) v * (v - 1) / 2) % MOD;
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}
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return (int) ans;
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}
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private int rev(int x) {
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int y = 0;
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while (x > 0) {
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y = y * 10 + x % 10;
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x /= 10;
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}
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return y;
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}
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}
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```
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### **C++**
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```cpp
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class Solution {
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public:
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const int mod = 1e9 + 7;
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int countNicePairs(vector<int>& nums) {
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unordered_map<int, int> cnt;
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for (int& x : nums) {
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int y = x - rev(x);
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cnt[y]++;
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}
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long long ans = 0;
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for (auto& [_, v] : cnt) {
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ans = (ans + 1ll * v * (v - 1) / 2) % mod;
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}
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return ans;
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}
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int rev(int x) {
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int y = 0;
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while (x) {
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y = y * 10 + x % 10;
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x /= 10;
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}
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return y;
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}
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};
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```
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### **Go**
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```go
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func countNicePairs(nums []int) (ans int) {
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const mod int = 1e9 + 7
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rev := func(x int) (y int) {
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for x > 0 {
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y = y*10 + x%10
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x /= 10
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}
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return
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}
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cnt := map[int]int{}
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for _, x := range nums {
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y := x - rev(x)
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cnt[y]++
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}
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for _, v := range cnt {
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ans = (ans + v*(v-1)/2) % mod
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}
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return
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}
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```
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### **...**

‎solution/1800-1899/1814.Count Nice Pairs in an Array/README_EN.md

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### **Python3**
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```python
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class Solution:
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def countNicePairs(self, nums: List[int]) -> int:
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def rev(x):
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y = 0
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while x:
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y = y * 10 + x % 10
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x //= 10
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return y
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cnt = Counter(x - rev(x) for x in nums)
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ans = 0
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mod = 10**9 + 7
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for v in cnt.values():
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ans = (ans + v * (v - 1) // 2) % mod
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return ans
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```
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### **Java**
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```java
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class Solution {
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private static final int MOD = (int) 1e9 + 7;
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public int countNicePairs(int[] nums) {
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Map<Integer, Integer> cnt = new HashMap<>();
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for (int x : nums) {
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int y = x - rev(x);
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cnt.put(y, cnt.getOrDefault(y, 0) + 1);
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}
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long ans = 0;
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for (int v : cnt.values()) {
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ans = (ans + (long) v * (v - 1) / 2) % MOD;
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}
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return (int) ans;
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}
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private int rev(int x) {
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int y = 0;
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while (x > 0) {
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y = y * 10 + x % 10;
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x /= 10;
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}
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return y;
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}
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}
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```
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### **C++**
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```cpp
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class Solution {
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public:
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const int mod = 1e9 + 7;
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int countNicePairs(vector<int>& nums) {
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unordered_map<int, int> cnt;
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for (int& x : nums) {
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int y = x - rev(x);
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cnt[y]++;
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}
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long long ans = 0;
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for (auto& [_, v] : cnt) {
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ans = (ans + 1ll * v * (v - 1) / 2) % mod;
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}
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return ans;
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}
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int rev(int x) {
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int y = 0;
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while (x) {
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y = y * 10 + x % 10;
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x /= 10;
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}
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return y;
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}
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};
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```
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### **Go**
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```go
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func countNicePairs(nums []int) (ans int) {
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const mod int = 1e9 + 7
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rev := func(x int) (y int) {
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for x > 0 {
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y = y*10 + x%10
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x /= 10
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}
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return
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}
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cnt := map[int]int{}
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for _, x := range nums {
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y := x - rev(x)
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cnt[y]++
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}
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for _, v := range cnt {
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ans = (ans + v*(v-1)/2) % mod
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}
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return
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}
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```
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### **...**

‎solution/1800-1899/1814.Count Nice Pairs in an Array/Solution.cpp

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class Solution {
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public:
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const int mod = 1e9 + 7;
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int countNicePairs(vector<int>& nums) {
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unordered_map<int, int> cnt;
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for (int& x : nums) {
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int y = x - rev(x);
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cnt[y]++;
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}
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long long ans = 0;
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for (auto& [_, v] : cnt) {
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ans = (ans + 1ll * v * (v - 1) / 2) % mod;
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}
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return ans;
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}
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int rev(int x) {
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int y = 0;
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while (x) {
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y = y * 10 + x % 10;
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x /= 10;
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}
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return y;
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}
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};

‎solution/1800-1899/1814.Count Nice Pairs in an Array/Solution.go

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func countNicePairs(nums []int) (ans int) {
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const mod int = 1e9 + 7
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rev := func(x int) (y int) {
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for x > 0 {
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y = y*10 + x%10
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x /= 10
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}
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return
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}
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cnt := map[int]int{}
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for _, x := range nums {
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y := x - rev(x)
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cnt[y]++
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}
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for _, v := range cnt {
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ans = (ans + v*(v-1)/2) % mod
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}
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return
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}

‎solution/1800-1899/1814.Count Nice Pairs in an Array/Solution.java

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class Solution {
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private static final int MOD = (int) 1e9 + 7;
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public int countNicePairs(int[] nums) {
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Map<Integer, Integer> cnt = new HashMap<>();
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for (int x : nums) {
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int y = x - rev(x);
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cnt.put(y, cnt.getOrDefault(y, 0) + 1);
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}
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long ans = 0;
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for (int v : cnt.values()) {
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ans = (ans + (long) v * (v - 1) / 2) % MOD;
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}
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return (int) ans;
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}
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private int rev(int x) {
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int y = 0;
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while (x > 0) {
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y = y * 10 + x % 10;
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x /= 10;
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}
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return y;
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}
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}

‎solution/1800-1899/1814.Count Nice Pairs in an Array/Solution.py

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class Solution:
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def countNicePairs(self, nums: List[int]) -> int:
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def rev(x):
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y = 0
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while x:
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y = y * 10 + x % 10
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x //= 10
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return y
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cnt = Counter(x - rev(x) for x in nums)
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ans = 0
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mod = 10**9 + 7
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for v in cnt.values():
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ans = (ans + v * (v - 1) // 2) % mod
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return ans

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