#include <bits/stdc++.h>
using namespace std;
const int N = 1005;
int dp[N][N]={0};
int main() {
    string s1, s2;
    cin >> s1 >> s2;
    int len1=s1.size(), len2=s2.size();
    for(int i=0; i<len1; i++) {
        dp[i][0]=0;
    }
    for(int j=0; j<len2; j++) {
        dp[0][j]=0;
    }
    for(int i=1; i<=len1; i++) {
        for(int j=1; j<=len2; j++) {
            if(s1[i-1]==s2[j-1]) {
                dp[i][j]=dp[i-1][j-1]+1;
            } else {
                dp[i][j]=max(dp[i-1][j], dp[i][j-1]);}
        }
    }
    cout << dp[len1][len2] << endl;
}

C :

#include "stdio.h"
#include "string.h"
int n,m;
char a[5002],b[5002];
int f[2][5001];
int max(int a,int b)
{
	if(a>b)
		return a;
	return b;
}
int main()
{
	int i,j;
	scanf("%s%s",a,b);
	n=strlen(a);
	m=strlen(b);
	for(i=1;i<=n;i++)
	{
		for(j=1;j<=m;j++)
		{
			if(a[i-1]==b[j-1])
				f[i%2][j]=f[(i-1)%2][j-1]+1;
			else
				f[i%2][j]=max(f[(i-1)%2][j],f[i%2][j-1]);
		}
	}
	printf("%d\n",f[n%2][m]);
	return 0;
}

C++ :

//最长公共子序列 
#include<iostream>
#include<fstream>
#include<string>
using namespace std;
const int N=1005;
int f[N][N]={0};
int main()
{
	//ifstream cin("lcs.in");
	//ofstream cout("lcs.out");
	string s1,s2;
	cin>>s1>>s2;
	int len1=s1.size(),len2=s2.size();
	for (int i=0;i<len1;i++) f[i][0]=0;
	for (int j=0;j<len2;j++) f[0][j]=0;
	for (int i=1;i<=len1;i++)
		for (int j=1;j<=len2;j++)
			if (s1[i-1]==s2[j-1])
				f[i][j]=f[i-1][j-1]+1;
			else f[i][j]=max(f[i-1][j],f[i][j-1]);
	cout<<f[len1][len2]<<endl;
	//system("pause");
	return 0;
}

Java :

import java.util.Scanner;


public class Main {
	static String s1,s2;
	static int[][] dp = new int[1005][1005];
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		while(in.hasNext()){
			s1 = in.next();
			s2 = in.next();
			solve();
		}
	}

	public static void solve() {
		int size1 = s1.length();
		int size2 = s2.length();
		if (size1 == 0 || size2 == 0)
			return ;
		for (int i = 1; i <= size1; i++) {
			for (int j = 1; j <= size2; j++) {
				if (s1.charAt(i - 1) == s2.charAt(j - 1))
					dp[i][j] = dp[i - 1][j - 1] + 1;
				else
					dp[i][j] = dp[i - 1][j] > dp[i][j - 1] ? dp[i - 1][j]
							: dp[i][j - 1];
			}
		}
		System.out.println(dp[size1][size2]);
	}
}