Go: package main

import (
	"fmt"
	"os"
	"strconv"
	"bufio"
	"strings"
	"sort"
)

// define
var (
	sc = bufio.NewScanner(os.Stdin)
)

func bordersInt(in_map [][]int, invalid int) [][]int{
	H, W := len(in_map), len(in_map[0])
	out_map := make([][]int, H+2)
	for h:=0; h<H+2; h++ {
		out_map[h] = make([]int, W+2)
		for w:=0; w<W+2; w++ {
			out_map[h][w] = invalid
		}
	}
	for h:=0; h<H; h++{
		for w:=0; w<W; w++{
			out_map[h+1][w+1] = in_map[h][w] 
		}
	}
	return out_map
}

func bordersString(in_map [][]string, invalid string) [][]string{
	H, W := len(in_map), len(in_map[0])
	out_map := make([][]string, H+2)
	for h:=0; h<H+2; h++ {
		out_map[h] = make([]string, W+2)
		for w:=0; w<W+2; w++ {
			out_map[h][w] = invalid
		}
	}
	for h:=0; h<H; h++{
		for w:=0; w<W; w++{
			out_map[h+1][w+1] = in_map[h][w] 
		}
	}
	return out_map
}

func scanIntLine(len int) []int{
	arr := make([]int, len)
	for i:=0; i<len; i++{
		sc.Scan()
		tmp, err := strconv.Atoi(sc.Text())
		if err == nil{
			arr[i] = tmp
		}
	}
	return arr
}

func scanStringLine(len int) []string{
	arr := make([]string, len)
	for i:=0; i<len; i++{
		sc.Scan()
		arr[i] = sc.Text()
	}
	return arr
}

func scanIntSplit(len int) []int{
	arr := make([]int, len)
	sc.Scan()
	for i, v := range strings.Split(sc.Text(), " "){
		tmp, err := strconv.Atoi(v)
		if err == nil{
			arr[i] = tmp
		}
	}
	return arr
}

func maxInt(args... int) int{
	sort.Ints(args)
	return args[len(args)-1]
}

func main(){
	buf := make([]byte, 0)
    sc.Buffer(buf, 1000000009)
	var n int 
	fmt.Scan(&n)
	dp := make([][]int, 1003)
	for i:=0; i<1003; i++ {
		dp[i] = make([]int, 1003)
	}
	input_lines := scanStringLine(2*n)
	for i:=0; i<n; i++ {
		S, T := input_lines[2*i], input_lines[2*i+1]
		lenS, lenT := len(S), len(T)
		for i:=1; i<lenS+1; i++ {
			for j:=1; j<lenT+1; j++ {
				if S[i-1] == T[j-1] {
					dp[i][j] = maxInt(dp[i-1][j-1]+1, dp[i-1][j], dp[i][j-1])
				} else {
					dp[i][j] = maxInt(dp[i-1][j], dp[i][j-1])
				}
			}
		}
		fmt.Println(dp[lenS][lenT])
	}
}

C++: #include <iostream>
#include <string>
using namespace std;
 
void lcs(string X, string Y) {
    int xLength = X.size();
    int yLength = Y.size();
 
    int dp[xLength + 10][yLength + 10];  
    int i,j;

    // initialize dp[][]
    for (i = 1; i <= xLength; i++)
        dp[i][0] = 0;
    for (i = 1; i <= yLength; i++)
        dp[0][i] = 0;
 
    for (i = 1; i <= xLength; i++){
        for (j = 1; j <= yLength; j++){
            // Because the original string is 0-based , so subtracted from 1
            if (X[i - 1] == Y[j - 1]) {
                dp[i][j] = dp[i-1][j-1] + 1;
            }else {
                dp[i][j] = max(dp[i-1][j], dp[i][j-1]);
            }
        }
    }
 
    // testing code: print out the dp[][]
    // cout << "j";
    // for (j = 1; j <= yLength; j++)
    //  cout << ' ' << j ;
    // cout << endl;
         
 
    // for (i = 1; i <= xLength; i++){
    //  cout << i << '.';
    //  for (j = 1; j <= yLength; j++){
    //      cout << dp[i][j] << ' ';
    //  }
    //  cout << endl;
    // }
 
    cout << dp[xLength][yLength] << endl;
}
 
int main() {
    int n , i;
    string X, Y;
 
    cin >> n;
    for (i = 0 ; i < n; i++ ) {
        cin >> X;
        cin >> Y;
        lcs(X, Y);
    }
 
    return 0;
 
}

C++: #include <iostream>
#include <string>
using namespace std;
int main(void){
    int n;
    cin >> n;
    for(int i = 0;i < n;i++){
        string X,Y;
        cin >> X >> Y;
        int L[X.length()+10][Y.length()+10];
        for(int j = 0;j < X.length()+10;j++){
            for(int k = 0;k < X.length()+10;k++){
                L[j][k] = 0;
            }
        }
        for(int j = 1;j<=X.length();j++){
            for(int k = 1;k<=Y.length();k++){
                if(Y[k] == X[j]){
                    L[j][k] = 1+L[j-1][k-1];
                }
                else{
                    L[j][k] = max(L[j-1][k],L[j][k-1]);
                }
            }
        }
        cout << L[X.length()][Y.length()] << endl;
    }
}

C++: #include<iostream>
#include<string>
#include<algorithm>
using namespace std;

int main(){
    int q;
    cin >> q;
    int dp[1001][1001] = {0};
    for(int i = 0; i < q; i++){
        bool flagx[1001] = {0}, flagy[1001] = {0};
        string S1, S2;
        cin >> S1 >> S2;
        const int m = S1.size();
        const int n = S2.size();
        for(int j = 0; j < m; j++){
            for(int k = 0; k < n; k++){
                if(j == 0 && k == 0) dp[j][k] = 0;
                else if(j == 0) dp[j][k] = dp[j][k-1];
                else if(k == 0) dp[j][k] = dp[j-1][k];
                else{
                    dp[j][k] = max(dp[j-1][k],dp[j][k-1]);
                }
                if(S1[j] == S2[k] && !flagx[j] && !flagy[k]) {
                    //cout << j << " " << k << " " << dp[j][k]++ <<endl;
                    dp[j][k]++;
                    flagx[j] = 1;
                    flagy[k] = 1;
                }
            }

        }
        cout << dp[m-1][n-1] << endl;
    }
}

C++: #include <iostream>
#include <cstring>
#include <algorithm>
#include <string>
using namespace std;

int q;
string X, Y;


int main(void) {
  int dp[1000][1000];
  cin >> q;
  for (int i = 0; i < q; i++) {
    cin >> X >> Y;

    dp[0][0] = X[0] == Y[0];
    for (int j = 1; j < Y.size(); j++) dp[0][j] = dp[0][j-1] || X[0] == Y[j];
    for (int j = 1; j < X.size(); j++) dp[j][0] = dp[j-1][0] || X[j] == Y[0];

    for (int j = 1; j < X.size(); j++) {
      for (int k = 1; k < Y.size(); k++) {
        if (X[j] == Y[k]) {
          dp[j][k] = dp[j-1][k-1] + 1;
        } else {
          dp[j][k] = max(dp[j-1][k], dp[j][k-1]);
        }
      }
    }

    cout << dp[X.size()-1][Y.size()-1] << endl;
  }
  return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<algorithm>
#include<vector>

using namespace std;

typedef pair<int,int> pii;

vector<pii> P;

string s,t,rev;

const int MAX_N = 1001;

int dp[MAX_N][MAX_N];

void trace(int i,int j){
	if(dp[i][j] == dp[i-1][j] && dp[i][j] == dp[i][j-1]){
		trace(i-1,j-1);	//??????????§????
	}else if(dp[i][j] == dp[i-1][j]){
		trace(i-1,j);	//???????§????
	}else if(dp[i][j] == dp[i][j-1]){
		trace(i,j-1);	//???????§????
	}else{
		rev += s[i-1];
		if(dp[i-1][j-1] == 0){
			return;
		}
		trace(i-1,j-1);	//??????????§????
	}
}
int main()
{
	string com;
	int n;
	cin >> n;
	for(int l=0;l<n;l++){
	cin >> s;
	cin >> t;
	for(int i=0;i<=s.length();i++){
		dp[i][0] = 0;
	}
	for(int i=0;i<=t.length();i++){
		dp[0][i] = 0;
	}
	for(int i=1;i<=s.length();i++){
		for(int j=1;j<=t.length();j++){
			if(s[i-1] == t[j-1]){
				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[s.length()][t.length()]);
	}
	/*
	trace(s.length(),t.length());
	for(int i=rev.length();i>0;i--){
		com += rev[i-1];
	}
	cout << com << "\n";	//????????±?????¨???????????????????????????
	*/
}