Go: package main

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

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 500001), 500000)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func main() {
	fp := os.Stdin
	if len(os.Args) > 1 {
		fp, _ = os.Open(os.Args[1])
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(os.Stdout)

	n := getNextInt(scanner)
	for i := 0; i < n; i++ {
		x := getNextString(scanner)
		y := getNextString(scanner)

		fmt.Fprintln(writer, lcs(x, y))
	}

	writer.Flush()
}

func lcs(x, y string) int {
	lx := len(x)
	ly := len(y)
	dp := make([][]int, lx+1)
	for i := 0; i <= lx; i++ {
		dp[i] = make([]int, ly+1)
	}
	for i := 0; i < lx; i++ {
		for ii := 0; ii < ly; ii++ {
			if x[i] == y[ii] {
				dp[i+1][ii+1] = dp[i][ii] + 1
				continue
			}
			dp[i+1][ii+1] = dp[i][ii+1]
			if dp[i+1][ii] > dp[i+1][ii+1] {
				dp[i+1][ii+1] = dp[i+1][ii]
			}
		}
	}
	return dp[lx][ly]
}

C++: /**
 * @copyright (c) 2020 Daisuke Hashimoto
 */

#include <bits/stdc++.h>
using namespace std;
using Pair = pair<int64_t, int64_t>;
constexpr int64_t kInf = INT64_MAX / 2L;

// std::cout << std::setprecision(20) << 1.1 << endl;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int64_t Q;
  cin >> Q;
  for (int64_t q = 0; q < Q; ++q) {
    string s, t;
    cin >> s >> t;
    const int64_t SL = static_cast<int64_t>(s.length());
    const int64_t TL = static_cast<int64_t>(t.length());
    vector<vector<int64_t>> dp(SL + 1, vector<int64_t>(TL + 1, 0));
    for (int64_t i = 1; i <= SL; ++i) {
      for (int64_t j = 1; j <= TL; ++j) {
        dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]);
        if (s[i - 1] == t[j - 1]) {
          dp[i][j] = max(dp[i][j], 1 + dp[i - 1][j - 1]);
        }
      }
    }
    cout << dp[SL][TL] << endl;
  }
  return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
#include<string>
#include<set>
#include<map>

using namespace std;

const int MAX_SIZE = 1000;

int LCS(string& X, string& Y,int dp[MAX_SIZE][MAX_SIZE], int X_pos, int Y_pos) {
	if (Y_pos == Y.length() || X_pos == X.length()) {
		return 0;
	}
	int res;

	if (dp[X_pos][Y_pos + 1] == -1) {
		dp[X_pos][Y_pos + 1] = LCS(X, Y, dp, X_pos, Y_pos + 1);
	}
	res = dp[X_pos][Y_pos + 1];

	for (int i = X_pos; i < X.length(); i++) {
		if (X[i] == Y[Y_pos]) {
			if (dp[i + 1][Y_pos + 1] == -1) {
				dp[i + 1][Y_pos + 1] = LCS(X, Y, dp, i + 1, Y_pos + 1);
			}
			res = max(dp[i + 1][Y_pos + 1] + 1, res);
		}
	}
	return res;
}

int main() {
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		string X, Y;
		int dp[MAX_SIZE][MAX_SIZE];

		cin >> X;
		cin >> Y;

		for (int i = 0; i < X.length() + 1; i++) {
			for (int j = 0; j < Y.length() + 1; j++) {
				dp[i][j] = -1;
			}
		}

		cout << LCS(X, Y, dp, 0, 0) << endl;
	}
	return 0;
}

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

using namespace std;

int main(){
  string X,Y;
  int n;
  cin>>n;
  int ans[n];
  int l=0;
  for(int m=0;m<n;m++){
  cin>>X>>Y;

  int N[X.size()+1][Y.size()+1];

  for(int i=0;i<=X.size();i++){
    for(int j=0;j<=Y.size();j++){

      N[i][j]=1;
}
  }

  /*
  for(int i=0;i<X.size();i++){
    cout<<X[i]<<endl;
  }

for(int i=0;i<Y.size();i++){
    cout<<Y[i];
  }
  */

  
for(int i=0;i<=X.size();i++){
  N[i][0]=0;
  }

for(int i=0;i<=Y.size();i++){
  N[0][i]=0;
  }

 int point;

  for(int i=1;i<=X.size();i++){
    for(int j=1;j<=Y.size();j++){
      if(X[i-1]==Y[j-1]){
	point=1;
	
      }else{
	point=0;
      }
       N[i][j]=max({N[i-1][j],N[i][j-1],N[i-1][j-1]+point});
       point=0;
}
   
  }
  ans[l]=N[X.size()][Y.size()];
  l++;
  // cout<<N[X.size()][Y.size()]<<endl;
  /*
  //answer
  for(int i=0;i<=X.size();i++){
    for(int j=0;j<=Y.size();j++){

      cout<<N[i][j]<<" ";
      if(j==Y.size()){
	cout<<endl;
      }
}
  }
  */

  }
  cout<<ans[0]<<endl;
 cout<<ans[1]<<endl;
 cout<<ans[2]<<endl;
}

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

int preX[1020][30];
int dp[1020];

int main() {
	int q;
	cin >> q;
	for(int t = 0; t < q; t++) {
		string X, Y;
		for(int i = 0; i < 1020; i++) {
			for(int j = 0; j < 30; j++) {
				preX[i][j] = 0;
			}
			dp[i] = 0;
		}
		cin >> X >> Y;
		for(int i = 0; i < X.size(); i++) {
			for(int j = 0; j < 30; j++) {
				preX[i+1][j] = preX[i][j];
			}
			if(i > 0)
				preX[i+1][X[i-1]-'a'] = i;
		}
		for(int i = 0; i < Y.size(); i++) {
			for(int j = (int)X.size()-1; j >= 0; j--) {
				if(Y[i] == X[j])
					for(int k = 0; k < 30; k++)
						dp[j+1] = max(dp[j+1], dp[preX[j+1][k]] + 1);
			}
		}
		int res = 0;
		for(int i = 0; i < 1020; i++)
			res = max(res, dp[i]);
		cout << res << endl;
	}
}

C++: #include <bits/stdc++.h>

using namespace std;

#define ll long long
typedef complex<double> P;

const int MAX_SIZE = 1001;
int q;
int dp[MAX_SIZE][MAX_SIZE] = {};

int main() {
  cin >> q;
  for (int i = 0; i < q; i++) {

    for (int j = 0; j < MAX_SIZE; j++) {
      dp[MAX_SIZE-1][0] = 0;
      dp[0][MAX_SIZE-1] = 0;
    }

    string a, b; cin >> a >> b;

    for (int j = 0; j < a.size(); j++) {
      for (int k = 0; k < b.size(); k++) {
        if(a[j] == b[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]);
        }
      }
    }

    cout << dp[a.size()][b.size()] << endl;
  }
}