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>
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;
}

C++: /**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author NikuKyabe
 */

#include <iostream>
#include <string>
#include <vector>
using namespace std;
#define int long long
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define REP(i,n)  FOR(i,0,(n))
typedef vector<int> vec;
typedef vector< vector<int> > mat;


class Longest_Common_Subsequence {
public:
	void solve(std::istream& in, std::ostream& out) {
	  int q;
	  in >> q;
	  REP(i, q){
	    string x,y;
	    in >> x >> y;
	    mat dp = mat(x.length()+1, vec(y.length()+1, 0));
	    REP(j,x.length())REP(k,y.length()){
	      if(x[j] == y[k]){
	        dp[j + 1][k + 1] = dp[j][k] + 1;
	      }
	      else{
	        dp[j + 1][k + 1] = max(dp[j][k + 1], dp[j + 1][k]);
	      }
	    }
	    out << dp[x.length()][y.length()] << endl;
	  }
	}
};


signed main() {
  ios::sync_with_stdio(false);
  cout.tie(0);
  cout << fixed;
	Longest_Common_Subsequence solver;
	std::istream& in(std::cin);
	std::ostream& out(std::cout);
	solver.solve(in, out);
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
static const int N=1001;
int lcs(string X,string Y){
  int c[N][N] = {};
  int m=X.size();
  int n=Y.size();

  int max1=0;
  X=' '+X;
  Y=' '+Y;

  //for(int i=1;i<=m;i++){
  //  c[i][0]=0;
  //}
  //for(int j=1;j<=n;j++){
  //  c[0][j]=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]);
      }
      max1=max(max1,c[i][j]);
    }
  }
  return max1;
}

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;
}

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

string s, t;
int dp[1001][1001];
int main()
{
    int p;
    cin >> p;
    while(p>0)
    {
        p--;
        cin >> s >> t;
        int n = s.size();
        int m = t.size();
        for (int i = 1; i <= n; i++)
            dp[i][0] = 0;
        for (int i = 1; i <= m; i++)
            dp[0][i] = 0;
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if (s[i - 1] == t[i - 1]) {
                    dp[i][j] = dp[i - 1][j - 1] + 1;
                }
                else if (dp[i - 1][j] >= dp[i][j - 1]) {
                    dp[i][j] = dp[i - 1][j];
                }
                else {
                    dp[i][j] = dp[i][j - 1];
                }
            }
        }
        cout << dp[n][m] << endl;
    }

}

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

static const int N = 1000;

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;
  C[0][0] = 0;
  for ( int i = 1; i <= m; i++ ) c[i][0] = 0;
  for ( int j = 1; j <= n; j++ ) c[0][j] = 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]);
    }
  }javascript:void(0)

  return maxl;
}

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;
}