Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	Q := sc.nextInt()
	for q := 0; q < Q; q++ {
		X, Y := sc.nextStr(), sc.nextStr()
		xLen, yLen := len(X), len(Y)
		dp := make([][]int, xLen+1)
		for i := 0; i <= xLen; i++ {
			dp[i] = make([]int, yLen+1)
		}
		for x := 0; x <= xLen; x++ {
			for y := 0; y <= yLen; y++ {
				if x == 0 || y == 0 {
					dp[x][y] = 0
				} else if X[x-1] == Y[y-1] {
					dp[x][y] = dp[x-1][y-1] + 1
				} else {
					dp[x][y] = max(dp[x-1][y], dp[x][y-1])
				}
			}
		}
		fmt.Fprintln(wtr, dp[xLen][yLen])
	}

	wtr.Flush()
}

C++: #include <bits/stdc++.h>
//----***やべーやつら***----
using namespace std;
#define int long long

//----***型定義***----
using ll = long long;
using P = pair<int,int>;

//----***Like a Pythonista***----
#define REP(ii,jj,nn) for (ll ii=jj;ii<(nn);ii++)
#define RREP(ii,nn,jj) for (ll ii = nn; jj<ii;ii--)
#define each(i,...) for (auto&& i:__VA_ARGS__)
#define ALL(vec) (vec).begin(),(vec).end()
#define sum(...) accumulate(ALL(__VA_ARGS__),0LL)
#define dsum(...) accumulate(ALL(__VA_ARGS__),0.0)
#define vec(type,name,...) vector<type> name(__VA_ARGS__)
template<class T> inline auto max(const T& a){ return *max_element(ALL(a)); }
template<class T> inline auto min(const T& a){ return *min_element(ALL(a)); }
inline ll gcd(ll a,ll b){if(b == 0) return a;return  gcd(b,a%b);}
inline ll lcm(ll a,ll b){ll g = gcd(a,b);return a / g * b;}

//----***定数***----
#define MOD 1000000007
#define INF 100000000000000000
#define EPS 1e-9
const vector<vector<int>> DXY={{-1,0},{1,0},{0,-1},{0,1}};

//----***パーツ***----
#define fr first
#define se second

//----***入出力***---
#define print(out) cout<< out  << "\n";
#define debug(var)  do{std::cerr << #var << " ↓ "<<"\n";view(var);}while(0);
#define dbg cerr<<"🥺🥺🥺🥺🥺🥺"<<endl;
template<typename T> void view(T e){std::cout << e << std::endl;}
template<typename T> void view(const std::vector<T>& v){for(const auto& e : v){ std::cout << e << " "; } std::cout << std::endl;}
template<typename T> void view(const std::vector<std::vector<T> >& vv){ for(const auto& v : vv){ view(v); } }

//----***初期時読み込み***----
struct initial{initial(){cin.tie(0); ios::sync_with_stdio(0); cout<<fixed<<setprecision(15);};}initial_;

vector<vector<int>>dp(30,vector<int>(50010,0));

signed main(){
  int N;cin>>N;
  vector<int> ans;
  REP(i,0,N){
    string S,T;cin>>S>>T;
    int s_size=S.size(),t_size=T.size();
    vector<vector<int>> dp(t_size+2,vector<int>(s_size+2));
    REP(i,1,t_size+1)REP(j,1,s_size+1){
      if(S.at(j-1)==T.at(i-1)){
        dp[i][j]=max(dp[i-1][j-1]+1,dp[i-1][j]);
      }
      else{
        dp[i][j]=max(dp[i][j-1],dp[i-1][j]);
      }
    }
    // debug(dp)
    ans.push_back(dp[t_size][s_size]);
  }
  each(a,ans){
    print(a)
  }

}

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

static const int N = 1000;
using namespace std;

int LCS(string X,string Y){
  int m,n;
  
  m = X.size();
  n = Y.size();
  
  int dp[N + 1][N + 1] = {0};
  
  X = ' ' + X;
  Y = ' ' + Y;

  for(int i = 1;i <= m;i++){
    for(int j = 1;j <= n;j++){
      if(X[i] == Y[j]){
	dp[i][j] = dp[i - 1][j - 1] + 1;
      }else{
	dp[i][j] = max(dp[i - 1][j],dp[i][j - 1]);
      }
    }
  }
  
  /*for(int i = 0;i < ax;i++){
    for(int j = 0;j < ay;j++){
      cout << dp[i][j] << " ";
    }
    cout << '\n';
    }*/
  
  return dp[m][n];
}

int main(){
  int q;
  string X,Y;
  
  cin >> q;
  
  for(int i = 0;i < q;i++){
    cin >> X >> Y;
    //cout << X.size() << " " << Y.size() << '\n';
    cout << LCS(X,Y) << '\n';
  }
  
  return 0;
}

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

int solve(std::string &x, std::string &y){
    int c[1001][1001] = {};
    int m = x.length();
    int n = y.length();

    //for(int i = 1; i <= m; ++i) c[i][0] = 0;                                                                                                                                                                                      
    //for(int i = 1; i <= n; ++i) c[0][i] = 0;                                                                                                                                                                                      
    int maxval = 0;
    x = ' ' + x;
    y = ' ' + y;
    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] = std::max(c[i][j - 1], c[i - 1][j]);
            }
            maxval = std::max(maxval, c[i][j]);
        }
    }
    return maxval;
}

int main(){
    int q;
    std::cin >> q;
    for(int i = 0; i < q; ++i){
        std::string x;
        std::string y;
        std::cin >> x;
        std::cin >> y;
        int res = solve(x, y);
        std::cout << res << "\n";
    }
    return 0;
}

C++: #include <bits/stdc++.h>
 
using namespace std;
typedef long long ll;
typedef vector<ll> vl ;
typedef pair<ll,ll> pl;
 
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define rep(i,N) for(int i=0; i < (int)N; i++)
#define all(v) (v).begin(),(v).end()
#define max(a,b) (a>b ? a : b)
#define min(a,b) (a<b ? a : b)
 
const int MOD = 998244353;
const int INF = 1000002;
const double PI =4*atan(1);
const double eps = 1e-7;
const long long oo = 1e18;

int resolve(string S, string T){
  int s = (int)S.size(), t = (int)T.size();
  vector<vector<int>> dp(s+1, vector<int>(t+1, 0));

  for(int i=0; i<s; i++){
    for(int j=0; j<t; j++){
      if(S[i]==T[j]) dp[i+1][j+1] = dp[i][j]+1;
      else dp[i+1][j+1] = max(dp[i+1][j], dp[i][j+1]);
    }
  }
  return dp[s][t];
}

int main(){
  int N;
  cin >> N;
  rep(i,N){
    string S, T;
    cin >> S >> T;
    cout << resolve(S, T) << endl;
  }
}