HDU 1159 Common Subsequence

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;

const int maxn=1111;
int dp[maxn][maxn];
char s[maxn],t[maxn];
int lens,lent;

int main()
{
    int i,j;
    while(~scanf("%s%s",s,t))
    {
        lens=strlen(s);
        lent=strlen(t);
        for(i=-1; i<lens; i++)
            for(j=-1; j<lent; j++)
            {
                if(i==-1||j==-1)
                {
                    dp[i+1][j+1]=0;
                    continue;
                }
                if(s[i]==t[j])
                    dp[i+1][j+1]=dp[i][j]+1;
                else
                    dp[i+1][j+1]=max(dp[i+1][j],dp[i][j+1]);
            }
        printf("%d\n",dp[lens][lent]);
    }
    return 0;
}