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++: #include<iostream>
#include<algorithm>
#include<string>
#include<cstring>
#include<sstream>
#include<iomanip>
#include<limits>
#include<deque>
#include<map>
#include<list>
#include<set>
#include <unordered_set>
#include<vector>
#include<cmath>
#include<cstdio>
#include<memory>
#include<bitset>
#include<stack>
#include<functional>
#include<queue>
#include<regex>
#include<time.h>

using namespace std;

#define YES cout<<"YES"<<endl
#define NO cout<<"NO"<<endl
#define Yes cout<<"Yes"<<endl
#define No cout<<"No"<<endl
#define yes cout<<"yes"<<endl
#define no cout<<"no"<<endl

#define Tof(x) (x) ? Yes : No
#define TOF(x) (x) ? YES : NO
#define tof(x) (x) ? yes : no

using ll = long long;

constexpr ll MOD = 1000000007;
constexpr ll INF = 1050000000;



/*for文でx,yを上下左右確認するやつだよ。正直使いづらいよ。

int dx[] = { 1,-1, 1,-1,0,1,-1, 0 };
int dy[] = { 1,-1,-1, 1,1,0, 0,-1 };


for (int i = 0; i < 4; i++) {
	int ny = y + dy[i];
	int nx = x + dx[i];
}

*/

/*繰り返し二乗法だよ。modもとってくれるよ。n^kをmodで割った余りでやってくれるよ。

ll POW_MOD(ll n, ll k, ll mod) {
	ll r = 1;

	for (; k > 0; k >>= 1) {
		if (k & 1) {
			r = (r * n) % mod;
		}
		n = (n * n) % mod;
	}
	return r;
}

*/

/*2重for文書くのめんどくなった時用だよ。

for (int i = 0; i < h; ++i) {
	for (int j = 0; j < w; ++j) {

	}
}

*/

struct node {
	int value;
	node* next;
	node(int value, node* next) : value(value), next(next) { }
};

#define index_of(as, x) distance(as.begin(), lower_bound(as.begin(), as.end(), x))

vector<int> lcs_hs(const vector<int>& a, const vector<int>& b) {
	const int n = a.size(), m = b.size();
	map< int, vector<int> > M;
	for (int j = m - 1; j >= 0; --j)
		M[b[j]].push_back(j);
	vector<int> xs(n + 1, INF); xs[0] = -INF;
	vector< node* > link(n + 1);
	for (int i = 0; i < n; ++i) {
		if (M.count(a[i])) {
			vector<int> ys = M[a[i]];
			for (int j = 0; j < ys.size(); ++j) {
				int k = index_of(xs, ys[j]);
				xs[k] = ys[j];
				link[k] = new node(b[ys[j]], link[k - 1]);
			}
		}
	}
	int l = index_of(xs, INF - 1) - 1;
	vector<int> c;
	for (node* p = link[l]; p; p = p->next)
		c.push_back(p->value);
	reverse(c.begin(), c.end());
	return c;
}


int main() {
	int n; cin >> n;

	for (int i = 0; i < n; i++) {
		vector<int> a, b;
		string s; cin >> s;
		for (int j = 0; j<s.size(); j++) {
			char x = s[j];
			a.push_back((int)x);
		}
		string t; cin >> t;
		for (int j = 0; j<t.size(); j++) {
			char y = t[j];
			b.push_back((int)y);
		}
		vector<int> c = lcs_hs(a, b);
		cout << c.size() << endl;
	}


	return 0;
}

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



int lcs(string x, string y){

  int m = x.length();
  int n = y.length();

  int c[m + 1][n + 1];

  for(int i = 1; i < m; i++){
    c[i][0] = 0;
  }
  for(int i = 1; i < n; i++){
    c[0][i] = 0;
  }

  for(int i = 1; i <= m; i++){
    for(int j = 1; j <= n; j++){
      if(x[i - 1] == y[j - 1]){
        c[i][j] = c[i - 1][j - 1] + 1;
      }
      else if(c[i - 1][j] > c[i][j - 1]){
        c[i][j] = c[i - 1][j];
      }
      else{
        c[i][j] = c[i][j - 1];
      }
    }

  }

  return c[m][n];
}

int main(){

  int q;

  string x, y;

  cin >> q;

  for(int i = 0; i < q; i++){
    cin >> x;
    cin >> y;
    cout << lcs(x, y) << endl;
  }



  return 0;
}

C++: #include <bits/stdc++.h>
#define rep(i,a,n) for(int i=a;i<n;i++)
#define repr(i,a,n) for(int i=a;i>=n;i--)
#define INF 999999999
#define pb(a) push_back(a)

using namespace std;
typedef pair<int, int> pii;
typedef long long int ll;
typedef vector<pii> VP;

int dy[]={0, 0, 1, -1};
int dx[]={1, -1, 0, 0};

int main() {
    int num; cin >> num;
    rep(k,0,num) {
        string s1,s2;
        cin >> s1 >> s2;

        int dp[1001][1001]; //s1???i??????????????§???s2???j??????????????§??§???LCS????±???????????????????
        int n = s1.length();
        int m = s2.length();
        rep(i,0,m+1) dp[0][i] = 0;

        rep(i,0,n) {
            rep(j,0,m) {
                if(s1[i]==s2[j]) dp[i+1][j+1] = dp[i][j] + 1;
                else dp[i+1][j+1] = max(dp[i][j+1], dp[i+1][j]);
            }
        }
        cout << dp[n][m] << endl;
    }
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
typedef long long int ll;

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

	int N; cin >> N;
	string s[310];
	for (int i = 0; i < 2*N; i+=2) {
		cin >> s[i] >> s[i + 1];
	}
	for (int l = 0; l < 2 * N; l += 2) {
		int dp[1010][1010];
		int m = 0;
		int i = 0;
		while (i < s[l].length()&&s[l][i]!=s[l+1][0]) {
			dp[i][0] = 0;
			i++;
		}
		while (i < s[l].length()) {
			dp[i][0] = 1;
			i++;
			m = 1;
		}
		i = 0;
		while (i < s[l+1].length() && s[l+1][i] != s[l][0]) {
			dp[0][i] = 0;
			i++;
		}
		while (i < s[l+1].length()) {
			dp[0][i] = 1;
			i++;
			m = 1;
		}
		for (i = 1; i < s[l].length(); i++) {
			for (int j = 1; j < s[l + 1].length(); j++) {
				dp[i][j] = dp[i - 1][j - 1];
				if (s[l][i] == s[l + 1][j])dp[i][j]++;
				dp[i][j] = max({ dp[i][j],dp[i][j - 1],dp[i - 1][j] });
				m = max(dp[i][j], m);
			}
		}
		cout << m << endl;
	}
}

C++: #include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int dp[1002][1002];

int main(){
	int n;cin >> n;
	string x, y;
	while(n--){
		cin >> x >> y;
		for(int i = 1;i <= x.size();i++){
			for(int j = 1;j <= y.size();j++){
				if(x[i-1] == y[j-1])dp[i][j] = dp[i-1][j-1] + 1;
				else dp[i][j] = max(dp[i-1][j], dp[i][j-1]);
			}
		}
		cout << dp[x.size()][y.size()] << endl;
	}
	return 0;
}