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feat: add solutions to lc problem: No.0247
No.0247.Strobogrammatic Number II
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‎solution/0200-0299/0247.Strobogrammatic Number II/README.md

Lines changed: 32 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -37,6 +37,22 @@
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<!-- 这里可写通用的实现逻辑 -->
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**方法一：递归**
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若长度为 $1$，则中心对称数只有 $0, 1, 8$；若长度为 $2$，则中心对称数只有 $11, 69, 88, 96$。
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我们设计递归函数 $dfs(u)$，其返回长度为 $u$ 的中心对称数。答案为 $dfs(n)$。
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若 $u$ 为 $0$，返回包含一个空串的列表，即 `[""]`；若 $u$ 为 $1$，返回列表 `["0", "1", "8"]`。
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若 $u$ 大于 $1$，我们对长度为 $u - 2$ 的所有中心对称数进行遍历，对于每个中心对称数 $v$，在其左右两侧分别添加 $1, 8, 6, 9$，即可得到长度为 `u` 的中心对称数。
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注意，如果 $u\neq n$，我们还可以在中心对称数的左右两侧分别添加 $0$。
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最终，我们将所有长度为 $n$ 的中心对称数返回即可。
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时间复杂度为 $O(4\times 2^ n)$。
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<!-- tabs:start -->
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### **Python3**
@@ -53,7 +69,7 @@ class Solution:
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return ['0', '1', '8']
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ans = []
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for v in dfs(u - 2):
56-
for l, r in [['1', '1'], ['8', '8'], ['6', '9'], ['9', '6']]:
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for l, r in ('11', '88', '69', '96'):
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ans.append(l + v + r)
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if u != n:
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ans.append('0' + v + '0')
@@ -68,6 +84,7 @@ class Solution:
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```java
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class Solution {
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private static final int[][] PAIRS = {{1, 1}, {8, 8}, {6, 9}, {9, 6}};
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private int n;
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public List<String> findStrobogrammatic(int n) {
@@ -83,13 +100,12 @@ class Solution {
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return Arrays.asList("0", "1", "8");
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}
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List<String> ans = new ArrayList<>();
86-
int[][] pairs = new int[][] {{1, 1}, {8, 8}, {6, 9}, {9, 6}};
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for (String v : dfs(u - 2)) {
88-
for (int[] p : pairs) {
104+
for (var p : PAIRS) {
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ans.add(p[0] + v + p[1]);
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}
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if (u != n) {
92-
ans.add("0" + v + "0");
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ans.add(0 + v + 0);
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}
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}
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return ans;
@@ -102,23 +118,21 @@ class Solution {
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```cpp
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class Solution {
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public:
105-
int n;
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const vector<pair<char, char>> pairs = {{'1', '1'}, {'8', '8'}, {'6', '9'}, {'9', '6'}};
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vector<string> findStrobogrammatic(int n) {
107-
this->n = n;
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function<vector<string>(int)> dfs = [&](int u) {
125+
if (u == 0) return vector<string>{""};
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if (u == 1) return vector<string>{"0", "1", "8"};
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vector<string> ans;
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for (auto& v : dfs(u - 2)) {
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for (auto& [l, r] : pairs) ans.push_back(l + v + r);
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if (u != n) ans.push_back('0' + v + '0');
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}
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return ans;
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};
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return dfs(n);
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}
110-
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vector<string> dfs(int u) {
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if (u == 0) return {""};
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if (u == 1) return {"0", "1", "8"};
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vector<string> ans;
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vector<vector<char>> pairs = {{'1', '1'}, {'8', '8'}, {'6', '9'}, {'9', '6'}};
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for (string v : dfs(u - 2)) {
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for (auto& p : pairs) ans.push_back({p[0] + v + p[1]});
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if (u != n) ans.push_back('0' + v + '0');
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}
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return ans;
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}
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};
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```
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‎solution/0200-0299/0247.Strobogrammatic Number II/README_EN.md

Lines changed: 16 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -39,7 +39,7 @@ class Solution:
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return ['0', '1', '8']
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ans = []
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for v in dfs(u - 2):
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for l, r in [['1', '1'], ['8', '8'], ['6', '9'], ['9', '6']]:
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for l, r in ('11', '88', '69', '96'):
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ans.append(l + v + r)
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if u != n:
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ans.append('0' + v + '0')
@@ -52,6 +52,7 @@ class Solution:
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```java
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class Solution {
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private static final int[][] PAIRS = {{1, 1}, {8, 8}, {6, 9}, {9, 6}};
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private int n;
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public List<String> findStrobogrammatic(int n) {
@@ -67,13 +68,12 @@ class Solution {
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return Arrays.asList("0", "1", "8");
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}
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List<String> ans = new ArrayList<>();
70-
int[][] pairs = new int[][] {{1, 1}, {8, 8}, {6, 9}, {9, 6}};
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for (String v : dfs(u - 2)) {
72-
for (int[] p : pairs) {
72+
for (var p : PAIRS) {
7373
ans.add(p[0] + v + p[1]);
7474
}
7575
if (u != n) {
76-
ans.add("0" + v + "0");
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ans.add(0 + v + 0);
7777
}
7878
}
7979
return ans;
@@ -86,23 +86,21 @@ class Solution {
8686
```cpp
8787
class Solution {
8888
public:
89-
int n;
89+
const vector<pair<char, char>> pairs = {{'1', '1'}, {'8', '8'}, {'6', '9'}, {'9', '6'}};
90+
9091
vector<string> findStrobogrammatic(int n) {
91-
this->n = n;
92+
function<vector<string>(int)> dfs = [&](int u) {
93+
if (u == 0) return vector<string>{""};
94+
if (u == 1) return vector<string>{"0", "1", "8"};
95+
vector<string> ans;
96+
for (auto& v : dfs(u - 2)) {
97+
for (auto& [l, r] : pairs) ans.push_back(l + v + r);
98+
if (u != n) ans.push_back('0' + v + '0');
99+
}
100+
return ans;
101+
};
92102
return dfs(n);
93103
}
94-
95-
vector<string> dfs(int u) {
96-
if (u == 0) return {""};
97-
if (u == 1) return {"0", "1", "8"};
98-
vector<string> ans;
99-
vector<vector<char>> pairs = {{'1', '1'}, {'8', '8'}, {'6', '9'}, {'9', '6'}};
100-
for (string v : dfs(u - 2)) {
101-
for (auto& p : pairs) ans.push_back({p[0] + v + p[1]});
102-
if (u != n) ans.push_back('0' + v + '0');
103-
}
104-
return ans;
105-
}
106104
};
107105
```
108106

‎solution/0200-0299/0247.Strobogrammatic Number II/Solution.cpp

Lines changed: 12 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -1,20 +1,18 @@
11
class Solution {
22
public:
3-
int n;
3+
const vector<pair<char, char>> pairs = {{'1', '1'}, {'8', '8'}, {'6', '9'}, {'9', '6'}};
4+
45
vector<string> findStrobogrammatic(int n) {
5-
this->n = n;
6+
function<vector<string>(int)> dfs = [&](int u) {
7+
if (u == 0) return vector<string>{""};
8+
if (u == 1) return vector<string>{"0", "1", "8"};
9+
vector<string> ans;
10+
for (auto& v : dfs(u - 2)) {
11+
for (auto& [l, r] : pairs) ans.push_back(l + v + r);
12+
if (u != n) ans.push_back('0' + v + '0');
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}
14+
return ans;
15+
};
616
return dfs(n);
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}
8-
9-
vector<string> dfs(int u) {
10-
if (u == 0) return {""};
11-
if (u == 1) return {"0", "1", "8"};
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vector<string> ans;
13-
vector<vector<char>> pairs = {{'1', '1'}, {'8', '8'}, {'6', '9'}, {'9', '6'}};
14-
for (string v : dfs(u - 2)) {
15-
for (auto& p : pairs) ans.push_back({p[0] + v + p[1]});
16-
if (u != n) ans.push_back('0' + v + '0');
17-
}
18-
return ans;
19-
}
2018
};

‎solution/0200-0299/0247.Strobogrammatic Number II/Solution.java

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
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class Solution {
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private static final int[][] PAIRS = {{1, 1}, {8, 8}, {6, 9}, {9, 6}};
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private int n;
34

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public List<String> findStrobogrammatic(int n) {
@@ -14,13 +15,12 @@ private List<String> dfs(int u) {
1415
return Arrays.asList("0", "1", "8");
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}
1617
List<String> ans = new ArrayList<>();
17-
int[][] pairs = new int[][] {{1, 1}, {8, 8}, {6, 9}, {9, 6}};
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for (String v : dfs(u - 2)) {
19-
for (int[] p : pairs) {
19+
for (var p : PAIRS) {
2020
ans.add(p[0] + v + p[1]);
2121
}
2222
if (u != n) {
23-
ans.add("0" + v + "0");
23+
ans.add(0 + v + 0);
2424
}
2525
}
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return ans;

‎solution/0200-0299/0247.Strobogrammatic Number II/Solution.py

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@ def dfs(u):
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return ['0', '1', '8']
88
ans = []
99
for v in dfs(u - 2):
10-
for l, r in [['1', '1'], ['8', '8'], ['6', '9'], ['9', '6']]:
10+
for l, r in ('11', '88', '69', '96'):
1111
ans.append(l + v + r)
1212
if u != n:
1313
ans.append('0' + v + '0')

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