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feat: add solutions to lc problem: No.0409
No.0409.Longest Palindrome
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‎solution/0400-0499/0409.Longest Palindrome/README.md

Lines changed: 64 additions & 57 deletions
Original file line numberDiff line numberDiff line change
@@ -47,18 +47,17 @@
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<!-- 这里可写通用的实现逻辑 -->
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50-
> 一个回文字符串，最多存在一个出现奇数次数的字符，
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**方法一：计数**
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52-
先统计所有字符出现的次数，通用的方式是哈希表。题目已说明只存在大小写字母（52 种可能），也可以使用数组来存储。
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一个合法的回文字符串，最多存在一个出现奇数次数的字符，其余字符出现次数均为偶数。
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而后，可分两种方式：
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因此，我们可以先遍历字符串 $s$，统计每个字符出现的次数，记录在数组或哈希表 $cnt$ 中。
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- 布尔变量
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- 累加出现次数为偶数的数值。
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- 对于奇数，第一次出现，完整累加；后续出现，则需要对次数 `-1` 去奇，再累加。
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- 计数器
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- 记录奇数出现的次数，最后的结果回文长度由 `s.length - count` 得知。
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- 如果只存在一个奇数，那么可以直接返回 `s.length`.
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然后，我们遍历 $cnt$，对于每个字符 $c$，如果 $cnt[c]$ 为偶数，则直接将 $cnt[c]$ 累加到答案 $ans$ 中；如果 $cnt[c]$ 为奇数，则将 $cnt[c] - 1$ 累加到 $ans$ 中，如果 $ans$ 为偶数，则将 $ans$ 增加 $1$。
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最后，我们返回 $ans$ 即可。
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时间复杂度 $O(n)$，空间复杂度 $O(C)$。其中 $n$ 为字符串 $s$ 的长度；而 $C$ 为字符集的大小，本题中 $C = 128$。
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<!-- tabs:start -->
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@@ -69,10 +68,12 @@
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```python
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class Solution:
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def longestPalindrome(self, s: str) -> int:
72-
n = len(s)
73-
counter = Counter(s)
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odd_cnt = sum(e % 2 for e in counter.values())
75-
return n if odd_cnt == 0 else n - odd_cnt + 1
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cnt = Counter(s)
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ans = 0
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for v in cnt.values():
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ans += v - (v & 1)
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ans += (ans & 1 ^ 1) and (v & 1)
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return ans
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```
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### **Java**
@@ -82,20 +83,62 @@ class Solution:
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```java
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class Solution {
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public int longestPalindrome(String s) {
85-
int[] counter = new int[128];
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for (char c : s.toCharArray()) {
87-
++counter[c];
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int[] cnt = new int[128];
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for (int i = 0; i < s.length(); ++i) {
88+
++cnt[s.charAt(i)];
8889
}
89-
int oddCnt = 0;
90-
for (int e : counter) {
91-
oddCnt += (e % 2);
90+
int ans = 0;
91+
for (int v : cnt) {
92+
ans += v - (v & 1);
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if (ans % 2 == 0 && v % 2 == 1) {
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++ans;
95+
}
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}
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int n = s.length();
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return oddCnt == 0 ? n : n - oddCnt + 1;
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return ans;
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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:
107+
int longestPalindrome(string s) {
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int cnt[128]{};
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for (char& c : s) {
110+
++cnt[c];
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}
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int ans = 0;
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for (int v : cnt) {
114+
ans += v - (v & 1);
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if (ans % 2 == 0 && v % 2 == 1) {
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++ans;
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}
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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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### **Go**
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```go
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func longestPalindrome(s string) (ans int) {
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cnt := [128]int{}
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for _, c := range s {
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cnt[c]++
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}
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for _, v := range cnt {
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ans += v - (v & 1)
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if ans&1 == 0 && v&1 == 1 {
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ans++
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}
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}
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return
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}
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```
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### **TypeScript**
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```ts
@@ -133,42 +176,6 @@ function longestPalindrome(s: string): number {
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}
134177
```
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136-
### **C++**
137-
138-
```cpp
139-
class Solution {
140-
public:
141-
int longestPalindrome(string s) {
142-
vector<int> counter(128);
143-
for (char c : s) ++counter[c];
144-
int oddCnt = 0;
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for (int e : counter) oddCnt += e % 2;
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int n = s.size();
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return oddCnt == 0 ? n : n - oddCnt + 1;
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}
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};
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```
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152-
### **Go**
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```go
155-
func longestPalindrome(s string) int {
156-
counter := make([]int, 128)
157-
for _, c := range s {
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counter[c]++
159-
}
160-
oddCnt := 0
161-
for _, e := range counter {
162-
oddCnt += e % 2
163-
}
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n := len(s)
165-
if oddCnt == 0 {
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return n
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}
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return n - oddCnt + 1
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}
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```
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### **Rust**
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```rust

‎solution/0400-0499/0409.Longest Palindrome/README_EN.md

Lines changed: 56 additions & 48 deletions
Original file line numberDiff line numberDiff line change
@@ -42,31 +42,75 @@
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```python
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class Solution:
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def longestPalindrome(self, s: str) -> int:
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n = len(s)
46-
counter = Counter(s)
47-
odd_cnt = sum(e % 2 for e in counter.values())
48-
return n if odd_cnt == 0 else n - odd_cnt + 1
45+
cnt = Counter(s)
46+
ans = 0
47+
for v in cnt.values():
48+
ans += v - (v & 1)
49+
ans += (ans & 1 ^ 1) and (v & 1)
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return ans
4951
```
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5153
### **Java**
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5355
```java
5456
class Solution {
5557
public int longestPalindrome(String s) {
56-
int[] counter = new int[128];
57-
for (char c : s.toCharArray()) {
58-
++counter[c];
58+
int[] cnt = new int[128];
59+
for (int i = 0; i < s.length(); ++i) {
60+
++cnt[s.charAt(i)];
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}
60-
int oddCnt = 0;
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for (int e : counter) {
62-
oddCnt += (e % 2);
62+
int ans = 0;
63+
for (int v : cnt) {
64+
ans += v - (v & 1);
65+
if (ans % 2 == 0 && v % 2 == 1) {
66+
++ans;
67+
}
6368
}
64-
int n = s.length();
65-
return oddCnt == 0 ? n : n - oddCnt + 1;
69+
return ans;
6670
}
6771
}
6872
```
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74+
### **C++**
75+
76+
```cpp
77+
class Solution {
78+
public:
79+
int longestPalindrome(string s) {
80+
int cnt[128]{};
81+
for (char& c : s) {
82+
++cnt[c];
83+
}
84+
int ans = 0;
85+
for (int v : cnt) {
86+
ans += v - (v & 1);
87+
if (ans % 2 == 0 && v % 2 == 1) {
88+
++ans;
89+
}
90+
}
91+
return ans;
92+
}
93+
};
94+
```
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96+
### **Go**
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98+
```go
99+
func longestPalindrome(s string) (ans int) {
100+
cnt := [128]int{}
101+
for _, c := range s {
102+
cnt[c]++
103+
}
104+
for _, v := range cnt {
105+
ans += v - (v & 1)
106+
if ans&1 == 0 && v&1 == 1 {
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ans++
108+
}
109+
}
110+
return
111+
}
112+
```
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70114
### **TypeScript**
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72116
```ts
@@ -104,42 +148,6 @@ function longestPalindrome(s: string): number {
104148
}
105149
```
106150

107-
### **C++**
108-
109-
```cpp
110-
class Solution {
111-
public:
112-
int longestPalindrome(string s) {
113-
vector<int> counter(128);
114-
for (char c : s) ++counter[c];
115-
int oddCnt = 0;
116-
for (int e : counter) oddCnt += e % 2;
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int n = s.size();
118-
return oddCnt == 0 ? n : n - oddCnt + 1;
119-
}
120-
};
121-
```
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### **Go**
124-
125-
```go
126-
func longestPalindrome(s string) int {
127-
counter := make([]int, 128)
128-
for _, c := range s {
129-
counter[c]++
130-
}
131-
oddCnt := 0
132-
for _, e := range counter {
133-
oddCnt += e % 2
134-
}
135-
n := len(s)
136-
if oddCnt == 0 {
137-
return n
138-
}
139-
return n - oddCnt + 1
140-
}
141-
```
142-
143151
### **Rust**
144152

145153
```rust

‎solution/0400-0499/0409.Longest Palindrome/Solution.cpp

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@@ -1,11 +1,17 @@
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class Solution {
22
public:
33
int longestPalindrome(string s) {
4-
vector<int> counter(128);
5-
for (char c : s) ++counter[c];
6-
int oddCnt = 0;
7-
for (int e : counter) oddCnt += e % 2;
8-
int n = s.size();
9-
return oddCnt == 0 ? n : n - oddCnt + 1;
4+
int cnt[128]{};
5+
for (char& c : s) {
6+
++cnt[c];
7+
}
8+
int ans = 0;
9+
for (int v : cnt) {
10+
ans += v - (v & 1);
11+
if (ans % 2 == 0 && v % 2 == 1) {
12+
++ans;
13+
}
14+
}
15+
return ans;
1016
}
1117
};

‎solution/0400-0499/0409.Longest Palindrome/Solution.go

Lines changed: 9 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -1,15 +1,13 @@
1-
func longestPalindrome(s string) int {
2-
counter := make([]int, 128)
1+
func longestPalindrome(s string) (ans int) {
2+
cnt := [128]int{}
33
for _, c := range s {
4-
counter[c]++
4+
cnt[c]++
55
}
6-
oddCnt := 0
7-
for _, e := range counter {
8-
oddCnt += e % 2
6+
for _, v := range cnt {
7+
ans += v - (v & 1)
8+
if ans&1 == 0 && v&1 == 1 {
9+
ans++
10+
}
911
}
10-
n := len(s)
11-
if oddCnt == 0 {
12-
return n
13-
}
14-
return n - oddCnt + 1
12+
return
1513
}

‎solution/0400-0499/0409.Longest Palindrome/Solution.java

Lines changed: 10 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,16 @@
11
class Solution {
22
public int longestPalindrome(String s) {
3-
int[] counter = new int[128];
4-
for (char c : s.toCharArray()) {
5-
++counter[c];
3+
int[] cnt = new int[128];
4+
for (int i = 0; i < s.length(); ++i) {
5+
++cnt[s.charAt(i)];
66
}
7-
int oddCnt = 0;
8-
for (int e : counter) {
9-
oddCnt += (e % 2);
7+
int ans = 0;
8+
for (int v : cnt) {
9+
ans += v - (v & 1);
10+
if (ans % 2 == 0 && v % 2 == 1) {
11+
++ans;
12+
}
1013
}
11-
int n = s.length();
12-
return oddCnt == 0 ? n : n - oddCnt + 1;
14+
return ans;
1315
}
1416
}

‎solution/0400-0499/0409.Longest Palindrome/Solution.py

Lines changed: 6 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,8 @@
11
class Solution:
22
def longestPalindrome(self, s: str) -> int:
3-
n = len(s)
4-
counter = Counter(s)
5-
odd_cnt = sum(e % 2 for e in counter.values())
6-
return n if odd_cnt == 0 else n - odd_cnt + 1
3+
cnt = Counter(s)
4+
ans = 0
5+
for v in cnt.values():
6+
ans += v - (v & 1)
7+
ans += (ans & 1 ^ 1) and (v & 1)
8+
return ans

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