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++: // 最長共通部分列
// O(|S||T|)

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <complex>
#include <cmath>
#include <limits>
#include <climits>
#include <ctime>
#include <cassert>
#include <numeric>
#include <functional>
#include <bitset>

using namespace std;
using lint = long long int;
long long int INF = 1001001001001001LL;
int inf = 1000000007;
long long int MOD = 1000000007LL;
double PI = 3.1415926535897932;

template<typename T1,typename T2>inline void chmin(T1 &a,const T2 &b){if(a>b) a=b;}
template<typename T1,typename T2>inline void chmax(T1 &a,const T2 &b){if(a<b) a=b;}

#define ALL(a) a.begin(),a.end()
#define RALL(a) a.rbegin(),a.rend()


int LongestCommonSubsequence(const string &s, const string &t) {
  int n = (int)s.size();
  int m = (int)t.size();

  vector<vector<int>> dp(n + 1, vector<int> (m + 1, 0));
  for(int i = 1; i <= n; i++) {
    for(int j = 1; j <= m; j++) {
      dp[i][j] = max(dp[i][j], dp[i - 1][j]);
      dp[i][j] = max(dp[i][j], dp[i][j - 1]);
      dp[i][j] = max(dp[i][j], dp[i - 1][j - 1]);
      if(s[i - 1] == t[j - 1]) dp[i][j] = max(dp[i][j], dp[i - 1][j - 1] + 1);
    }
  }
  
  return dp[n][m];
}


int main() {
  int q; cin >> q;
  for(int i = 0; i < q; i++) {
    string s, t; cin >> s >> t;
    cout << LongestCommonSubsequence(s, t) << endl;
  }
  return 0;
}

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

const int N = 1000;

int lcs(string x, string y);

int main(){
  string s1,s2;
  int n;

  cin >> n;

  for(int i = 0; i < n; i++){
    cin >> s1 >> s2;
    cout << lcs(s1,s2) << endl;
  }
  
  return 0;
}

int lcs(string x, string y){
  int c[N+1][N+1];
  int m = x.size();
  int n = y.size();
  int maxl = 0;
  x = ' ' + x;
  y = ' ' + y;

  for(int i = 0; i <= m; i++) c[i][0] = 0;
  for(int i = 1; i <= n; i++) c[0][i] = 0;

  for(int i = 1; i <= m; i++){
    for(int j = 1; j <= n; j++){
      if(x[i] == y[j]) c[i][j] = c[i-1][j-1]+1;
      else c[i][j] = max(c[i-1][j], c[i][j-1]);

      maxl = max(maxl, c[i][j]);
    }
  }
  return maxl;
}

C++: #include <cstdio>
#include <cstring>
#include <algorithm>

#define rep(i, n) for(int i = 0; i < (n); ++i)

using namespace std;

int n, m;
char s[1001];
char t[1001];
int dp[1001][1001];

int main(){
	int q;
	scanf("%d", &q);
	rep(z, q){
		scanf("%s%s", s, t);
		n = strlen(s);
		m = strlen(t);

		rep(i, n + 1){
			dp[i][0] = 0;
		}
		rep(i, m + 1){
			dp[0][i] = 0;
		}
		for(int i = 1; i <= n; ++i){
			for(int j = 1; j <= m ; ++j){
				dp[i][j] = max(dp[i - 1][j - 1] + (s[i - 1] == t[j - 1]), max(dp[i][j - 1], dp[i - 1][j]));
			}
		}
		printf("%d\n", dp[n][m]);
	}
	return 0;
}

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

int q;

int main(void) {
    cin >> q;

    for (int i = 0; i < q; ++i) {
        string X;
        string Y;

        cin >> X >> Y;

        int xlen = X.size();
        int ylen = Y.size();

        X = ' ' + X;
        Y = ' ' + Y;

        int lcs[1010][1010] = {};

        lcs[0][0] = 0;

        for (int x = 1; x <= xlen; ++x) {
            for (int y = 1; y <= ylen; ++y) {

                if (X[x] == Y[y]) {
                    lcs[x][y] = lcs[x - 1][y - 1] + 1;
                }
                else {
                    lcs[x][y] = max(lcs[x - 1][y], lcs[x][y - 1]);
                }
            }
        }

        cout << lcs[xlen][ylen] << endl;
    }
    
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;


int main(int argc, char *argv[]){
  int n;
  cin >> n;
  for (int r = 0; r < n; r++) {

    string x, y;
    cin >> x >> y;
    string dp[y.length() + 1][x.length() + 1];

    for (int i = 0; i < y.length(); i++) {
      for (int j = 0; j < x.length(); j++) {
        if(y[i] == x[j]){
          dp[i + 1][j + 1] = dp[i][j] + y[i];
        }else{
          dp[i + 1][j + 1] = max(dp[i + 1][j], dp[i][j + 1]);
        }
      }
    }
    int ans = 0;
    for (int i = 0; i < n; i++) {
      ans = max(ans, dp[y.length()][i].length());
    }
    std::cout << ans << std::endl;
  }
  return 0;
}

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

int main(){
    int n;
    cin>>n;
    for(int cnt=0;cnt<n;++cnt){
        int lngst_cmn[1001][1001]={0};
        string x,y;
        cin>>x>>y;

        for(size_t i=1;i<=x.size();++i){
            for(size_t j=1;j<=y.size();++j){
                string subx=x.substr(0,i),suby=y.substr(0,j);
                if(subx[i-1]==suby[j-1]){
                    lngst_cmn[i][j]=1+lngst_cmn[i-1][j-1];
                }
                else {
                    lngst_cmn[i][j]=(lngst_cmn[i-1][j]>lngst_cmn[i][j-1] ? lngst_cmn[i-1][j]:lngst_cmn[i][j-1]);
                }
            }
        }

        cout<<lngst_cmn[x.size()][y.size()]<<"\n";
    }
}

C++: #include<iostream>
#include<string>
#include<cstring>
#include<algorithm>
#define MAX_N 1000
int dp[MAX_N][MAX_N];
int solve(std::string s,std::string t){
        
        memset(dp,0,sizeof(dp));
        int n,m;
        n=s.size(),m=t.size();
        for(int i=0;i<n;i++){
                for(int j=0;j<m;j++){
                        if(s[i]==t[j])
                                dp[i+1][j+1]=dp[i][j]+1;
                        else
                                dp[i+1][j+1]=std::max(dp[i][j+1],dp[i+1][j\
]);
                }
        }
        return dp[n][m];
}

int main(){
        int q;
        std::cin>>q;
std::string s,t;
        for(int i=0;i<q;i++){
                
                std::cin >> s>>t;
                std::cout << solve(s,t) << std::endl;
        }
        return 0;
}