銆怢eetCode銆?. Longest Palindromic Substring

Posted 2021-01-26

鏍囩锛?a href='http://www.mamicode.com/so/1/string' title='string'>string   log   code   link   inpu   longest   max   bst   private   

Difficulty: Medium

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Description

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

Example 1:

Input: "babad"
Output: "bab"
Note: "aba" is also a valid answer.

Example 2:

Input: "cbbd"
Output: "bb"

Intuition

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Solution

    public String longestPalindrome(String s) {
        if(s==null || s.length()<=0)
            return s;
        int start=0;
        int end=0;
        for(int i=0;i<s.length();i++){
            int len1=expand(s,i,i);
            int len2=expand(s,i,i+1);
            int len=Math.max(len1,len2);
            if(len>end-start){
                start=i-(len-1)/2;
                end=i+len/2;
            }
        }
        return s.substring(start,end+1);
    }
    
    private int expand(String s,int l,int r){
        while(l>=0 && r<s.length() && s.charAt(l)==s.charAt(r)){
            l--;
            r++;
        }
        return r-l-1;
    }

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Complexity

Time complexity : O(n^2)

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Space complexity :  O(1)

What I鈥榲e learned

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