LeetCode OJ 5 Longest Palindromic Substring

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https://leetcode.com/problems/longest-palindromic-substring/

感觉也许O(n)算法可以搞定，于是DP之，各种胡思乱想，于是各种BUG 。。。。。写死了，然后O(n*n)过掉的，搜下题解，然后发现一个打脸的事情，TM我写过博客http://blog.csdn.net/u011026968/article/details/26093495

就是这个O(n)算法啊，TMD 真是一朝不做ACM，各种算法全忘光

O(n)算法如下，没的说，裸地暴力

#include <cstdio>#include <cstring>#include <iostream>#include <string>#include <cstring>;using namespace std;class Solution {public:    string longestPalindrome(string s) {        int st=0,mx=1;        int dp[2005];        if(s.size() == 0)return "";        dp[0]=1;        for(int i=0;i<s.size();i++){            if(i+1<s.size()){                int cnt=0,flag=0;                if(s[i] == s[i+1]){                    cnt=2;                    flag=1;                    for(int j=i-1;j>=0 && j+cnt+1<s.size();j--){                        if(s[j] == s[j+cnt+1])cnt+=2;                        else break;                    }                    dp[i]=cnt;                    cnt=1;                    for(int j=i-1;j>=0 && j+cnt+1<s.size();j--){                        if(s[j] == s[j+cnt+1])cnt+=2;                        else break;                        //cout << i << "  " << j << "*" << cnt << endl;                    }                    if(cnt > dp[i])dp[i]=cnt;                    //cout << i << "  " << j << "*" << cnt << endl;                }else{                    cnt=1;                    for(int j=i-1;j>=0 && j+cnt+1<s.size();j--){                        if(s[j] == s[j+cnt+1])cnt+=2;                        else break;                    }                    dp[i]=cnt;                }                if(dp[i]>mx){                    /*if(flag){                        st = i-dp[i]/2+1;                    }else{                        st = i-dp[i]/2;                    }*/                     st = i-(dp[i]+1)/2+1;                    mx = dp[i];                }            }else{                dp[i]=1;            }            //mx = max(mx, dp[i]);        }        //cout << st << "  " << mx << endl;        return s.substr(st,mx);    }};int main(){    freopen("5in.txt","r",stdin);    string s;    Solution so;    while(cin >> s){        cout << so.longestPalindrome(s) << endl;    }    return 0;}

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