美团2017年CodeM大赛-初赛A轮 合并回文子串(区间dp)

题目

思路来源

https://blog.nowcoder.net/n/51d6684184b64b1399859ad5a22cbb5f

题解

hdu2205原题警告，牛客开启的每日一题活动，这两天貌似是dp，

至少区间dp是我不会的，之前没见过四维的区间dp

邓老师的讲解的确清楚明白啊，%西工大学姐

代码

#include<bits/stdc++.h>
using namespace std;
const int N=52;
bool dp[N][N][N][N];
char s[N],t[N];
int T,n,m;
int main(){
	scanf("%d",&T);
	while(T--){
		memset(dp,false,sizeof dp);
		scanf("%s%s",s+1,t+1);
		n=strlen(s+1),m=strlen(t+1);
		int ans=0;
		for(int len1=0;len1<=n;++len1){
			for(int len2=0;len2<=m;++len2){
				for(int l1=1;l1+len1-1<=n;++l1){
					int r1=l1+len1-1;
					for(int l2=1;l2+len2-1<=m;++l2){
						int r2=l2+len2-1;
						if(len1+len2<=1){
							dp[l1][r1][l2][r2]=1;
						}
						else{
							if(s[l1]==s[r1]&&len1>=1)dp[l1][r1][l2][r2]|=dp[l1+1][r1-1][l2][r2];//r1-1>=l1+1-1 
							if(t[l2]==t[r2]&&len2>=1)dp[l1][r1][l2][r2]|=dp[l1][r1][l2+1][r2-1];//r2-1>=l2+1-1
							if(s[l1]==t[r2]&&len1&&len2)dp[l1][r1][l2][r2]|=dp[l1+1][r1][l2][r2-1];//r1>=l1+1-1 r2-1>=l2-1
							if(t[l2]==s[r1]&&len1&&len2)dp[l1][r1][l2][r2]|=dp[l1][r1-1][l2+1][r2];//r1-1>=l1-1 r2>=l2+1-1
						}
						if(dp[l1][r1][l2][r2])ans=max(ans,len1+len2);
					}
				}
			}
		} 
		printf("%d\n",ans);
	}
	return 0;
}