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++: /**
 *    author  : 𝒌𝒚𝒐𝒎𝒖𝒌𝒚𝒐𝒎𝒖𝒑𝒖𝒓𝒊𝒏
 *    created : 2020-03-03 00:50:37
**/

#include <iostream>
#include <deque>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <complex>
#include <numeric>
#include <bitset>
#include <cassert>
#include <cctype>
#include <iomanip>
#include <random>
#include <utility>
#include <chrono>

using namespace std;

using int64 = long long;

template<class T> using binary_heap = std::priority_queue<T, std::vector<T>, std::greater<T>>;
template<class T> std::ostream& operator<<(std::ostream& os, const std::vector<T>& vec) { os << '{'; size_t n = vec.size(); for (size_t i = 0; i < n; ++i) { os << vec[i]; if (i != n - 1) os << ','; } os << '}'; return os; }
template<class T, class U> std::ostream& operator<<(std::ostream& os, const std::pair<T, U>& p) { return os << '{' << p.first << " " << p.second << '}'; }
template<class T, class U> std::ostream& operator<<(std::ostream& os, const std::map<T, U>& mp) { os << '{'; for (auto it = mp.begin(); it != mp.end(); ++it) { os << '{' << it->first << ':' << it->second << '}'; if (it != --mp.end()) os << ','; } os << '}'; return os; }
template<class T> std::ostream& operator<<(std::ostream& os, const std::set<T>& st) { os << '{'; for (auto it = st.begin(); it != st.end(); ++it) { os << *it; if (it != --st.end()) os << ','; } os << '}'; return os; }
template<class T> std::istream& operator>>(std::istream& is, std::vector<T>& vec) { size_t n = vec.size(); for (size_t i = 0; i < n; ++i) is >> vec[i]; return is; }

#define all(_) begin(_), end(_)
#define rall(_) rbegin(_), rend(_)

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]: ", debug_out(__VA_ARGS__)
#else
#define debug(...) 1728
#endif

void debug_out() { std::cerr << '\n'; }

template <class Head, class... Tail>
void debug_out(Head&& head, Tail&&... tail) {
  std::cerr << head;
  if (sizeof...(Tail) != 0) std::cerr << ", ";
  debug_out(std::forward<Tail>(tail)...);
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  int q; cin >> q;

  while (q--) {
    string s, t; cin >> s >> t;
    int n = s.size(), m = t.size();
    vector<vector<int>> dp(n + 1, vector<int>(m + 1, 0));
    dp[0][0] = 0;
    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] = max(dp[i + 1][j], dp[i][j + 1]);
        }
      }
    }
    cout << dp[n][m] << '\n';
  };

  return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<string>
#define MAX 1001
using namespace std;

string x, y;

int c[MAX][MAX];
int lcs(int m, int n);

int main() {
	int i, q, n, m;
	cin >> q;
	for (i = 0; i < q; i++) {
		cin >> x >> y;
		cout << lcs(x.length(), y.length()) << endl;
	}
	return 0;
}

int lcs(int m, int n) {
	int i, j, maxl = 0;
	c[0][0] = 0;
	for (i = 1; i <= m; i++)c[i][0] = 0;
	for (j = 1; j <= n; j++)c[0][j] = 0;
	for (i = 1; i <= m; i++) {
		for (j = 1; j <= n; j++) {
			if (x[i - 1] == y[j - 1])c[i][j] = c[i - 1][j - 1] + 1;
			else c[i][j] = max(c[i][j - 1], c[i - 1][j]);
			maxl = max(maxl, c[i][j]);
		}
	}
	return maxl;
}

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;
  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]);
    }
  }

  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;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#define MAX 1000
using namespace std;

int LCS() {
    int i, j, maxl;
    string X, Y;
    int C[MAX+1][MAX+1];

    cin >> X >> Y;
    size_t X_len = X.length();
    size_t Y_len = Y.length();

    for (i=0; i<=X_len; i++) {
        for (j=0; j<=Y_len; j++) {
            if (i==0 || j==0) C[i][j]=0;
            else {
                if (X[i]==Y[j]) {
                    C[i][j]=C[i-1][j-1]+1;
                    maxl = max(C[i][j], maxl);
                } else C[i][j]=max(C[i-1][j], C[i][j]);
            }
        }
    }

    return maxl;
}

int main() {
    int n, i;
    
    cin >> n;
    for (i=0; i<n; i++) {
        printf("%d\n", LCS());
    }

    return 0;
}

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;
}