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给定一个字符串 s,找到 s 中最长的回文子串。你可以假设 s 的最大长度为 1000。
示例 1:
输入: "babad"
输出: "bab"
注意: "aba" 也是一个有效答案。
示例 2:
输入: "cbbd"
输出: "bb"
来源:力扣(LeetCode)
链接:https://leetcode-cn.com/problems/longest-palindromic-substring
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字符串回文很容易想到双指针,但回文串可能为奇数串,也可能是偶数串,所以当为奇数串时,双指针left和right相等,当为偶数串时,left和right相邻。接着就是枚举了,回文串的中点从0到最后,记录maxLen。返回值需要malloc,从字符串s中拷贝可以用strncpy库函数。
int findCenter(char *s, int left, int right, int len) {
int count = 0;
while((left >= 0) && (right <= len)) {
if(s[left] != s[right]) {
break;
}
count++;
left--;
right++;
}
count = right - left - 1;
return count;
}
#define MAX(a, b) ((a) > (b)) ? (a) : (b)
char * longestPalindrome(char * s){
int len = strlen(s);
int i;
int count;
int maxCount = 1;
int start = 0;
char *out;
int len1;
int len2;
out = (char *)malloc(1024);
memset(out, 0, 1024);
if (len == 0) {
return out;
}
for(i = 0; i < len-1; i++) {
len1 = findCenter(s, i, i, len);
len2 = findCenter(s, i, i+1, len);
count = MAX(len1, len2);
if(count > maxCount) {
start = i - (count - 1)/2;
maxCount = count;
}
}
strncpy(out, s+start, maxCount);
return out;
}