5. Longest Palindromic Substring

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example:

Input: “babad”

Output: “bab”

Note: “aba” is also a valid answer.
Example:

Input: “cbbd”

Output: “bb”

自己写的代码：
参照了： http://blog.csdn.net/hopeztm/article/details/7932245

public class Solution {    public char[] preProcess(String s){        int n = s.length();        if(n == 0){            char[] ch1 = new char[2];            ch1[0] = '^';            ch1[1] = '$';            return ch1;        }else{            char[] ch2 = new char[n+n+3];            int curIndex = 0;            ch2[curIndex++] = '^';            for(int i = 0;i < n; i++){                ch2[curIndex++] = '#';                ch2[curIndex++] = s.charAt(i);            }             ch2[curIndex++] = '#';            ch2[curIndex++] = '$';            return ch2;        }    }    public String longestPalindrome(String s) {        char[] ss = preProcess(s);        int n = ss.length;        int[] p = new int[n];        int cntrl = 0;        int right = 0;        for(int i = 1;i < n - 1;i++){            int i_mirror = cntrl + cntrl - i;            p[i] = (right > i) ? Math.min(right - i,p[i_mirror]) : 0;            while(ss[i + p[i] + 1] == ss[i - p[i] - 1])                p[i]++;            if(i + p[i] > right){                cntrl = i;                right = i + p[i];            }        }        int maxLen = 0;        int indexOfCntrl = 0;        for(int i = 1; i < n - 1;i++){            if(p[i] > maxLen){                maxLen = p[i];                indexOfCntrl = i;            }        }        return s.substring((indexOfCntrl - maxLen - 1)/2,(indexOfCntrl + maxLen - 1)/2);    }}

另外还有比这个简介的多的代码：

public class Solution {    public String longestPalindrome(String s) {    if(s==null){        return "";    }   char[] arr = s.toCharArray();      int max = 0;      int maxi = 0;      int maxj = 0;      for(int i = 0; i< arr.length;){          int i1 = getFarestSameElementIndex(arr,i);          int dist = getDistance(arr,i,i1);          int index1 = i-dist;          int index2 = i1 + dist;          int l = index2 - index1;          if(l>max){                  max = l;              maxi = index1;              maxj = index2;          }          i = i1+1;      }      return s.substring(maxi, maxj+1);}private int getDistance(char[] arr,int index1,int index2){    int i1 = index1-1;    int i2 = index2+1;    int dist = 0;    while(i1>=0&&i2<arr.length){        if(arr[i1]==arr[i2]){            dist++;        }else{            break;        }        i1--;i2++;    }    return dist;}private int getFarestSameElementIndex(char[] arr, int index){    for(int i = index+1;i<arr.length;i++){        if(arr[i]!=arr[index]){            return i-1;        }    }    return arr.length-1;}}