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(){
	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<cstdio>

using namespace std;

int m[1500][1500];
int main(){
  int n;
  cin>>n;
  char A[1500];
  char B[1500];
  for(int i=0;i<n;i++){
    cin>>A;
    cin>>B;
    int x;
    int y;
    for(x=0;A[x]!='\0';x++){
      for(y=0;B[y]!='\0';y++){
	if(A[x]==B[y]){
	  m[x+1][y+1]=m[x][y]+1;
	}
	else {
	  if(m[x][y+1]>m[x+1][y]){
	    m[x+1][y+1]=m[x][y+1];
	  }
	  else m[x+1][y+1]=m[x+1][y];
	}
      }
    }
    cout<<m[x][y]<<endl;

  }

  
  return 0;
}

C++: // ALDS1_10_C.cpp
// Dynamic Programming - Longest Common Subsequence

#include <iostream>
#include <vector>
#include <string>
using namespace std;

int LCS(string s, string t)
{
    int res = 0;
    if (s.empty() || t.empty())
        return res;
    int s_len = s.size();
    int t_len = t.size();
    int len = min(s_len, t_len);
//    int lcs[s_len][t_len];
    vector<vector<int>> lcs(s_len, vector<int>(t_len));
    bool found = false;
    for (int i = 0; i < s_len; i++) {
        if (s[i] == t[0] || found) {
            lcs[i][0] = 1;
            found = true;
        }
    }
    found = false;
    for (int j = 0; j < t_len; j++) {
        if (s[0] == t[j] || found) {
            lcs[0][j] = 1;
            found = true;
        }
    }
    for (int i = 1; i < s_len; i++) {
        for (int j = 1; j < t_len; j++) {
            if (s[i] == t[j]) {
                lcs[i][j] = 1 + lcs[i-1][j-1];
            }
            else {
                lcs[i][j] = max(lcs[i-1][j], lcs[i][j-1]);
            }
        }
    }
    return lcs[s_len - 1][t_len - 1];
}

int main()
{
    int n;
    cin >> n;
    string s, t;
    while (n--) {
        cin >> s >> t;
        int res = LCS(s, t);
        cout << res << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <string>
#include <algorithm>

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

using namespace std;

static const int N = 10000;

int lcs(string X, string Y);

int main(void){
	string s1, s2;
	int n; cin >> n;
	int i;
	REP(i, n) {
		cin >> s1 >> s2;
		cout << lcs(s1, s2) << endl;
	}
	return 0;
}

// longest common sequence
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;
	int i, j;
	FOR(i, 1, m + 1) FOR(j, 1, n + 1) {
		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++: #define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstdlib>
#include <string>
#include <iostream>
#include <queue>

using namespace std;

const char *X, *Y;
int X_length, Y_length;
bool alreadySeenTable[256];
int table_lcs[1001][1001];

int lcs(int x_begin, int y_begin) {
	int i, j, to;
	int max = 0;
	int v_lcs;
	
	if (table_lcs[x_begin][y_begin] != -1) {
		return table_lcs[x_begin][y_begin];
	}
	
	for (i = 0; i < 256; i++) {
		alreadySeenTable[i] = false;
	}
	i = x_begin;
	j = y_begin;
	to = Y_length-1;
	while(i <= X_length-1) {
		bool found = false;
		while (j <= to) {
			if (X[i] == Y[j]) {
				v_lcs = lcs(i + 1, j + 1) + 1;
				if (v_lcs > max) {
					max = v_lcs;
				}
				found = true;
				break;
			}
			else {
				j++;
			}
		}
		if (found == false) {
			i++;
			j = y_begin;
		}
		else {
			i++;
			to = j - 1;
			j = y_begin;
		}
	}
	return table_lcs[x_begin][y_begin] = max;
}

int main() {

	int N;
	cin >> N;
	string stringX, stringY;

	for (int i = 1; i <= N; i++) {
		for (int i = 0; i < 1001; i++) {
			for (int j = 0; j < 1001; j++) {
				table_lcs[i][j] = -1;
			}
		}
		cin >> stringX >> stringY;
		X = stringX.c_str();
		X_length = stringX.size();
		Y = stringY.c_str();
		Y_length = stringY.size();
		printf("%d\n", lcs(0, 0));
	}
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define MAX 2000
#define NOTFOUND -1
int Max = 0;
// nまでの文字列をいくつか選んで最長共通部を作ったときの長さ
//int dp[MAX];

bool 
IsInTargetString(string strFind, string strTgt)
{
    int idx;
    string strTmp = strTgt;

    for (int i = 0; i < strFind.size(); i++)
    {
        idx = strTgt.find(strFind[i]);
        if (idx != string::npos) {
            strTmp = strTgt.substr(idx+1);
            // cout << "idx = " << idx << " strFind = " << strFind
            // << " strTmp = " << strTmp <<  "\n";
        } else {
            return false;
        }
        strTgt = strTmp;
    }
    //cout <<  "\n";
    return true;
}

int
SearchCommonSubsequence(string strSet1, string strSet2)
{
    //vector<vector<bool>> dp(MAX, vector<bool>(MAX));

    // dp[i+1][j+1] = strSet1のi 文字目までとstrSet2のj文字目まででの LCS の長さ
    vector<vector<int>> dp(MAX, vector<int>(MAX));
    dp[0][0] = 0;
    string strRes = "";


    for (int i = 0; i < strSet1.size(); i++)
    {
        for (int j = 0; j < strSet2.size(); j++)
        {
            if(strSet1[i] == strSet2[j]) {
                dp[i+1][j+1] = max({dp[i][j] + 1,dp[i+1][j], dp[i][j+1]});
            } else {
                dp[i+1][j+1] = max(dp[i+1][j], dp[i][j+1]);
            }
        }
    }
        
    // for(int i=0; i<strSet1.size(); i++) {
    //     string strTmp = strRes;
    //     strTmp += strSet1[i];

    //     //if(strSet2.find(strTmp) != string::npos) {
    //     if(IsInTargetString(strTmp, strSet2)) {
    //         // 見つかった場合は更新a
    //         strRes = strTmp;
    //     } else {
    //         // 見つからなかった場合はそのまま
    //     }
    //     dp[i] = strRes.size();
    //     //cout << strRes << ", " << strSet1[i] << "\n";
    // }

    //auto itr = std::max_element(dp.begin(), dp.end());
    //return *itr;
    return dp[strSet1.size()][strSet2.size()];
}

int main()
{
    string strSet1, strSet2;
    int n;

    cin >> n;
    for (int i = 0; i < n; i++)
    {
        cin >> strSet1 >> strSet2;

        if(strSet1.size() > strSet2.size()) swap(strSet1, strSet2);
        cout << SearchCommonSubsequence(strSet1, strSet2) << "\n";
    }    
    return 0;
}