Go: package main

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

var sc = bufio.NewScanner(os.Stdin)

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func lcs(a, b string) int {
	lenA := len(a)
	lenB := len(b)
	dp := make([][]int, lenA+1)
	for i := range dp {
		dp[i] = make([]int, lenB+1)
	}

	for i := 1; i <= lenA; i++ {
		for j := 1; j <= lenB; j++ {
			if a[i-1] == b[j-1] {
				dp[i][j] = dp[i-1][j-1] + 1
			} else {
				dp[i][j] = max(dp[i][j-1], dp[i-1][j])
			}
		}
	}
	return dp[lenA][lenB]
}

func main() {
	n := scanInt()
	w := bufio.NewWriter(os.Stdout)
	for i := 0; i < n; i++ {
		a := scanString()
		b := scanString()
		fmt.Fprintln(w, lcs(a, b))
	}
	w.Flush()
}

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

using namespace std;
#define rep(i, n) for (ll i = 0; i < (n); ++i)
//#define rep(i, n) for (int i = 0; i < (n); ++i)
#define sz(x) ll(x.size())
//typedef long long ll;
typedef long long ll;
//typedef pair<int, int> P;
//typedef pair<ll, ll> P;
//const double INF = 1e10;
const ll INF = 10e15;
const ll MINF = -10e10;
//const int INF = INT_MAX / 100;
#define cmin(x, y) x = min(x, y)
#define cmax(x, y) x = max(x, y)


//ifstream myfile("~/Downloads/02.txt");
//ofstream outfile("log.txt");
//outfile << setw(6) << setfill('0') << prefecture << setw(6) << setfill('0') << rank << endl;
// std::cout << std::bitset<8>(9);

//typedef priority_queue<P, vector<P>, greater<P> > PQ_ASK;
const int mod = 1000000007;
const double PI = 3.14159265358979323846;

typedef pair<ll, ll> P;


string to_upper(string str) {
    int diff = 'a' - 'A';
    for (int i = 0; i < str.size(); i++) {
        char c = str[i];
        if ('A' <= c && c <= 'Z') {
            c += diff;
            str[i] = c;
        }
    }
    return str;
}


int main() {

    int n;
    cin >> n;

    rep(k, n) {

        string s1, s2;
        cin >> s1 >> s2;
        vector<vector<pair<int, pair<int, int> > > > dp(s1.size() + 1,
                                                        vector<pair<int, pair<int, int> > >(s2.size() + 1));
        for (int i = 0; i <= s1.size(); i++) {
            for (int j = 0; j <= s2.size(); j++) {
                if (i == 0 || j == 0) {
                    dp[i][j] = make_pair(0, make_pair(-1, -1));
                } else {
                    dp[i][j] = dp[i][j - 1];
                    if (dp[i][j].first < dp[i - 1][j].first) {
                        dp[i][j] = dp[i - 1][j];
                    }
                    if (s1[i - 1] == s2[j - 1] && dp[i][j].first < dp[i - 1][j - 1].first + 1) {
                        dp[i][j] = make_pair(dp[i - 1][j - 1].first + 1, make_pair(i - 1, j - 1));
                    }
                }
            }
        }
        vector<char> subseq_stack;
        for (int i = s1.size(), j = s2.size(); i > 0 && j > 0;) {
            pair<int, int> next = dp[i][j].second;
            //make_pair(i,j) = next;
            i = next.first;
            j = next.second;
            if (i < 0 || j < 0) break;
            subseq_stack.push_back(s1[i]); // s1[i] == s2[j]
        }
        cout << subseq_stack.size() << endl;
    }
}

C++: #include<iostream>
#include<algorithm>
#include<cstdio>
#include<string>
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 <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxx = 1010;
int c[maxx][maxx];

int lcs(char s1[],char s2[]) {
	int m = strlen(s1), n = strlen(s2);
	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 (s1[i] == s2[j])
				c[i][j] = c[i - 1][j - 1] + 1;
			else
				c[i][j] = max(c[i - 1][j], c[i][j - 1]);
		}
	}
	return c[m][n];
}
int main()
{
	char s1[maxx], s2[maxx];
	int t;
	scanf("%d", &t);
	getchar();
	for (int i = 0; i < t; i++) {
		scanf("%s %s", s1, s2);
		printf("%d\n", lcs(s1,s2));
	}

	return 0;
}

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

int main(){
    int q;
    cin >> q;
    int dp[1001][1001] = {0};
    for(int i = 0; i < q; i++){
        string S1, S2;
        cin >> S1 >> S2;
        const int m = S1.size();
        const int n = S2.size();
        for(int j = 0; j < m; j++){
            bool flag = 1;
            for(int k = 0; k < n; k++){
                if(j == 0 && k == 0) dp[j][k] = 0;
                else if(j == 0) dp[j][k] = dp[j][k-1];
                else if(k == 0) dp[j][k] = dp[j-1][k];
                else{
                    dp[j][k] = max(dp[j-1][k],dp[j][k-1]);
                }
                if(S1[j] == S2[k] && flag) {
                    //cout << j << " " << k << " " << dp[j][k]++ <<endl;
                    dp[j][k]++;
                    flag = 0;
                }
            }
        }
        cout << dp[m-1][n-1] << endl;
    }
}

C++: //
//  main.cpp
//  longest_common_subsequence
//
//  Created by ???????????? on 2017/10/17.
//  Copyright ?? 2017 ????????????. All rights reserved.
//

#include <iostream>
#include <stdio.h>
#include <string.h>

using namespace std;

char X[1005];
char Y[1005];

void lcs(){
    size_t m = strlen(X);
    size_t n = strlen(Y);
    int c[m+1][n+1];
    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 if(c[i-1][j] >= c[i][j-1]){
                c[i][j] = c[i-1][j];
            }
            else{
                c[i][j] = c[i][j-1];
            }
        }
    }
    cout << c[m][n] << endl;
//    cout << c[m+1][n+1] << endl;
}

int main(int argc, const char * argv[]) {
    int n, i;
    scanf("%d", &n);
    for (i = 0; i < n; i++){
        scanf("%s", X);
        scanf("%s", Y);
        lcs();
    }
//    std::cout << "Hello, World!\n";
    return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <cstring>
#include <cctype>
#include <cmath>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <list>
#include <stdio.h>
#include <string.h>
#include <cstdlib>
#include <math.h>
#include <bitset>
#include <iterator>
#include <iomanip>
#include <sstream>
#define INF 2000000000
using namespace std;
int dx[4]={1,0,-1,0},dy[4]={0,1,0,-1};
#define sym cout<<"---------"<<endl;
#define ll long long
#define PL pair<long long, long long>
#define P pair<int,int>
#define mk make_pair
#define en endl
#define WHITE 0
#define BLACK 2
#define GRAY 1
#define RE return 0
#define int ll

int dp[1005][1005];

signed main(){
  int n;
  cin>>n;
  for(int i=0; i<n; i++){
    string s1,s2;
    cin>>s1>>s2;
    s1=" "+s1;
    s2=" "+s2;
    for(int i=0; i<=s1.size(); i++) for(int j=0; j<=s2.size(); j++) dp[i][j]=0;
    for(int i=1; i<s1.size(); i++){
      for(int j=1; j<s2.size(); j++){
        if(s1[i]==s2[j]) dp[i][j]=dp[i-1][j-1]+1;
        else dp[i][j]=max(dp[i-1][j],dp[j-1][i]);
      }
    }
    cout<<dp[s1.size()-1][s2.size()-1]<<en;
  }
}