Longest Palindromic Substring

题目

Given a string S,
find the longest palindromic substring in S.
You may assume that the maximum length of S is
1000, and there exists one unique longest palindromic substring.

方法

以时间换空间的方法。 子串[i, j] 是回文串的要求是： 字符(i) == 字符(j) 且子串[i + 1, j - 1]也是回文串。每次将结果保存。

public String longestPalindrome(String s) {
if (s == null) {
return null;
}
if (s.length() <= 1) {
return s;
}
int len = s.length();
boolean[][] status = new boolean[len][len];
for (int interval = 0; interval < len; interval++) {
for (int i = 0; i < len - interval; i++) {
int j = i + interval;
if (i == j) {
status[i][j] = true;
} else if (s.charAt(i) == s.charAt(j)) {
if (i + 1 < j - 1) {
if (status[i + 1][j - 1] == true) {
status[i][j] = true;
}
} else {
status[i][j] = true;
}
}
}
}

int left = 0;
int right = 0;
for (int interval = 0; interval < len; interval++) {
for (int i = 0; i < len - interval; i++) {
int j = i + interval;
if (status[i][j] == true) {
left = i;
right = j;
break;
}
}
}
return s.substring(left, right + 1);

}