Go: package main

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

// define
var (
	sc = bufio.NewScanner(os.Stdin)
)

func bordersInt(in_map [][]int, invalid int) [][]int{
	H, W := len(in_map), len(in_map[0])
	out_map := make([][]int, H+2)
	for h:=0; h<H+2; h++ {
		out_map[h] = make([]int, W+2)
		for w:=0; w<W+2; w++ {
			out_map[h][w] = invalid
		}
	}
	for h:=0; h<H; h++{
		for w:=0; w<W; w++{
			out_map[h+1][w+1] = in_map[h][w] 
		}
	}
	return out_map
}

func bordersString(in_map [][]string, invalid string) [][]string{
	H, W := len(in_map), len(in_map[0])
	out_map := make([][]string, H+2)
	for h:=0; h<H+2; h++ {
		out_map[h] = make([]string, W+2)
		for w:=0; w<W+2; w++ {
			out_map[h][w] = invalid
		}
	}
	for h:=0; h<H; h++{
		for w:=0; w<W; w++{
			out_map[h+1][w+1] = in_map[h][w] 
		}
	}
	return out_map
}

func scanIntLine(len int) []int{
	arr := make([]int, len)
	for i:=0; i<len; i++{
		sc.Scan()
		tmp, err := strconv.Atoi(sc.Text())
		if err == nil{
			arr[i] = tmp
		}
	}
	return arr
}

func scanStringLine(len int) []string{
	arr := make([]string, len)
	for i:=0; i<len; i++{
		sc.Scan()
		arr[i] = sc.Text()
	}
	return arr
}

func scanIntSplit(len int) []int{
	arr := make([]int, len)
	sc.Scan()
	for i, v := range strings.Split(sc.Text(), " "){
		tmp, err := strconv.Atoi(v)
		if err == nil{
			arr[i] = tmp
		}
	}
	return arr
}

func maxInt(args... int) int{
	sort.Ints(args)
	return args[len(args)-1]
}

func main(){
	buf := make([]byte, 0)
    sc.Buffer(buf, 1000000009)
	var n int 
	fmt.Scan(&n)
	dp := make([][]int, 1003)
	for i:=0; i<1003; i++ {
		dp[i] = make([]int, 1003)
	}
	input_lines := scanStringLine(2*n)
	for i:=0; i<n; i++ {
		S, T := input_lines[2*i], input_lines[2*i+1]
		lenS, lenT := len(S), len(T)
		for i:=1; i<lenS+1; i++ {
			for j:=1; j<lenT+1; j++ {
				if S[i-1] == T[j-1] {
					dp[i][j] = dp[i-1][j-1]+1
				} else if S[i-1] != T[j-1] && dp[i-1][j] > dp[i][j-1] {
					dp[i][j] = dp[i-1][j]
				} else {
					dp[i][j] = dp[i][j-1]
				}
				// if S[i-1] == T[j-1] {
				// 	dp[i][j] = maxInt(dp[i-1][j-1]+1, dp[i-1][j], dp[i][j-1])
				// } else {
				// 	dp[i][j] = maxInt(dp[i-1][j], dp[i][j-1])
				// }
			}
		}
		fmt.Println(dp[lenS][lenT])
	}
}

C++: 
#define REP(i, t, n)  for (int i = t; i < n; i++)
#define ALL(n)        (n).begin(),(n).end()
#include <limits.h>
#include <stdio.h>
#include <cmath>
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <map>
#include <queue>
#include <deque>
#include <functional>
#include <algorithm>
#include <cstring>
#include <unordered_map>
#include <numeric>

using namespace std;

typedef bool               BOOL;
typedef short              WORD;
typedef unsigned short     U_WORD;
typedef long               DWORD;
typedef unsigned long      U_DWORD;
typedef long long          QWORD;
typedef unsigned long long U_QWORD;

#define LEN_MAX (1000)
DWORD dpLCS[LEN_MAX + 1][LEN_MAX + 1];

void initDpTable(DWORD maxI, DWORD maxJ)
{
	REP(i, 0, maxI + 1) {
		REP(j, 0, maxJ + 1) {
			dpLCS[i][j] = 0;
		}
	}

}

void solve_main()
{
	DWORD dwNum;
	string str1, str2;
	cin >> dwNum;
	REP(loop, 0, dwNum) {
		cin >> str1;
		cin >> str2;
		initDpTable(str1.length(), str2.length());

		REP(i, 1, (str1.length() + 1)) {
			REP(j, 1, (str2.length() + 1)) {
				if (str1[i - 1] == str2[j - 1]) {
					dpLCS[i][j] = dpLCS[i - 1] [j - 1] + 1;
				} else {
					dpLCS[i][j] = max(dpLCS[i - 1][j], dpLCS[i][j - 1]);
				}
			}
		}
		cout << dpLCS[str1.length()][str2.length()] << endl;
	}
}

int main()
{
#ifdef FOR_IDE
	ifstream in("input.txt");
	cin.rdbuf(in.rdbuf());
#endif

	solve_main();
	return 0;
}

C++: //   _/                _/                 _/_/_/   _/
//_/_/_/_/   _/_/   _/_/_/_/   _/_/    _/       _/_/
// _/     _/    _/   _/     _/    _/  _/_/_/     _/
//_/     _/    _/   _/     _/    _/  _/    _/   _/
// _/_/   _/_/       _/_/   _/_/      _/_/     _/
#include<iostream>
#include<algorithm>
#include<cmath>
#include<iomanip>
#include<set>
#include<map>
#include<queue>
#include<vector>
#include<random>
using namespace std;
typedef long long ll;
const int MOD=1e9+7;
const double pi=3.14159265358979323846;
const int inf=1e9;
const ll INF=1e18;
int main() {
  cin.tie(0),cout.tie(0);
  ios::sync_with_stdio(false);
  int q;
  cin >> q;
  while(q--) {
    string s,t;
    cin >> s >> t;
    int dp[s.size()+5][t.size()+5]={};
    for(int i=1; i<=s.size(); i++) {
      for(int j=1; j<=t.size(); j++) {
        if(s[i-1]==t[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[s.size()][t.size()] << endl;
  }
 }

C++: #include <iostream>
#include <string>
using namespace std;
static const int MAX = 1001;

void lcs(string X, string Y) {
	int dp[MAX][MAX];  
	int i,j;

	int xLength = X.size();
	int yLength = Y.size();


	// initialize dp[][]
	for (i = 1; i <= xLength; i++)
		dp[i][0] = 0;
	for (i = 1; i <= yLength; i++)
		dp[0][i] = 0;

	for (i = 1; i <= xLength; i++){
		for (j = 1; j <= yLength; j++){
			// Because the original string is 0-based , so subtracted from 1
			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]);
			}
		}
	}

	// testing code: print out the dp[][]
	cout << "j";
	for (j = 1; j <= yLength; j++)
		cout << ' ' << j ;
	cout << endl;
		

	for (i = 1; i <= xLength; i++){
		cout << i << '.';
		for (j = 1; j <= yLength; j++){
			cout << dp[i][j] << ' ';
		}
		cout << endl;
	}

	cout << dp[xLength][yLength] << endl;
}

int main() {
	int n , i;
	string X, Y;

	cin >> n;
	for (i = 0 ; i < n; i++ ) {
		cin >> X;
		cin >> Y;
		lcs(X, Y);
	}

	return 0;

}

C++: 
#include<bits/stdc++.h>
using namespace std;
#define mx 1007
string a,b;
int dp[mx][mx];
bool visited[mx][mx];

void init(int n)
{
    for(int i=0;i<n;i++)
    for(int j=0;j<n;j++)
    {
        visited[i][j]=false;
    }
}

int lcs(int i,int j)
{
    if(i==a.size() || j==b.size())
    {
        return 0;
    }

    if(visited[i][j])return dp[i][j];

    int ans=0;
    if(a[i]==b[j])
        ans=1+lcs(i+1,j+1);
    else ans+=max(lcs(i+1,j),lcs(i,j+1));

    dp[i][j]=ans;
    visited[i][j]=true;
    return dp[i][j];
}

int main()
{


 int n;
 cin>>n;
 while(n--)
 {
     cin>>a>>b;
     init(max(a.size(),b.size()));
     cout<<lcs(0,0)<<endl;
 }






    return 0;
}