poj 1458(最长公共子序列)

入门题。

有条件控制的状态转移　　

if(s[i]==j[i]) dp[i][j]=dp[i-1][j-1]+1;

else dp[i][j]=max(dp[i-1][j],dp[i][j-1]);

Common Subsequence

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 31866		Accepted: 12457

Description

A subsequence of a given sequence is the given sequence with some elements (possible none) left out. Given a sequence X = < x1, x2, ..., xm > another sequence Z = < z1, z2, ..., zk > is a subsequence of X if there exists a strictly increasing sequence < i1, i2, ..., ik > of indices of X such that for all j = 1,2,...,k, x_ij = zj. For example, Z = < a, b, f, c > is a subsequence of X = < a, b, c, f, b, c > with index sequence < 1, 2, 4, 6 >. Given two sequences X and Y the problem is to find the length of the maximum-length common subsequence of X and Y.

Input

The program input is from the std input. Each data set in the input contains two strings representing the given sequences. The sequences are separated by any number of white spaces. The input data are correct.

Output

For each set of data the program prints on the standard output the length of the maximum-length common subsequence from the beginning of a separate line.

Sample Input

abcfbc         abfcab
programming    contest 
abcd           mnp

Sample Output

4
2
0

Source

Southeastern Europe 2003

 

#include <stdio.h>
#include <string.h>
#include <iostream>
using namespace std;
#define N 1010

char s[N],t[N];
int dp[N][N];

int main()
{
    while(scanf("%s%s",s+1,t+1)!=EOF)
    {
        memset(dp,0,sizeof(dp));
        int n = strlen(s+1);
        int m = strlen(t+1);
        for(int i=1;i<=n;i++)
            for(int j=1;j<=m;j++)
            {
                if(s[i]==t[j])
                {
                    dp[i][j]=dp[i-1][j-1]+1;
                }
                else
                    dp[i][j]=max(dp[i][j-1],dp[i-1][j]);
            }
        printf("%d\n",dp[n][m]);
    }
    return 0;
}