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++: #include <bits/stdc++.h>
using namespace std;
#define MAX 2000
#define NOTFOUND -1
int Max = 0;
// nまでの文字列をいくつか選んで最長共通部を作ったときの長さ
//int dp[MAX];

bool 
IsInTargetString(string strFind, string strTgt)
{
    int idx;
    string strTmp = strTgt;

    for (int i = 0; i < strFind.size(); i++)
    {
        idx = strTgt.find(strFind[i]);
        if (idx != string::npos) {
            strTmp = strTgt.substr(idx+1);
            // cout << "idx = " << idx << " strFind = " << strFind
            // << " strTmp = " << strTmp <<  "\n";
        } else {
            return false;
        }
        strTgt = strTmp;
    }
    //cout <<  "\n";
    return true;
}

int
SearchCommonSubsequence(string strSet1, string strSet2)
{
    //vector<vector<bool>> dp(MAX, vector<bool>(MAX));

    // dp[i+1][j+1] = strSet1のi 文字目までとstrSet2のj文字目まででの LCS の長さ
    vector<vector<int>> dp(MAX, vector<int>(MAX));
    dp[0][0] = 0;
    string strRes = "";


    for (int i = 0; i < strSet1.size(); i++)
    {
        for (int j = 0; j < strSet2.size(); j++)
        {
            if(strSet1[i] == strSet2[j]) {
                dp[i+1][j+1] = max({dp[i][j] + 1,dp[i+1][j], dp[i][j+1]});
            } else {
                dp[i+1][j+1] = max(dp[i+1][j], dp[i][j+1]);
            }
        }
    }
        
    // for(int i=0; i<strSet1.size(); i++) {
    //     string strTmp = strRes;
    //     strTmp += strSet1[i];

    //     //if(strSet2.find(strTmp) != string::npos) {
    //     if(IsInTargetString(strTmp, strSet2)) {
    //         // 見つかった場合は更新a
    //         strRes = strTmp;
    //     } else {
    //         // 見つからなかった場合はそのまま
    //     }
    //     dp[i] = strRes.size();
    //     //cout << strRes << ", " << strSet1[i] << "\n";
    // }

    //auto itr = std::max_element(dp.begin(), dp.end());
    //return *itr;
    return dp[strSet1.size()][strSet2.size()];
}

int main()
{
    string strSet1, strSet2;
    int n;

    cin >> n;
    for (int i = 0; i < n; i++)
    {
        cin >> strSet1 >> strSet2;

        if(strSet1.size() > strSet2.size()) swap(strSet1, strSet2);
        cout << SearchCommonSubsequence(strSet1, strSet2) << "\n";
    }    
    return 0;
}

C++: #include <iostream>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <functional>
#include <vector>
#include <list>
#include <queue>
#include <deque>
#include <stack>
#include <map>
#include <set>
#include <bitset>
#include <tuple>
#include <cassert>
#include <exception>
#include <iomanip>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> P;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<string> vs;
typedef vector<P> vp;
#define rep(i,a,n) for(ll i = (a);i < (n);i++)
#define per(i,a,n) for(ll i = (a);i > (n);i--)
#define lep(i,a,n) for(ll i = (a);i <= (n);i++)
#define pel(i,a,n) for(ll i = (a);i >= (n);i--)
#define clr(a,b) memset((a),(b),sizeof(a))
#define pb push_back
#define mp make_pair
#define all(c) (c).begin(),(c).end()
#define sz size()
#define print(X) cout << (X) << endl
#define fprint(NUM,X) cout << fixed << setprecision(NUM) << (X) << endl
#define fprints(NUM,X,Y) cout << fixed << setprecision(NUM) << (X) << " " << (Y) << endl
const ll INF = 1e+9+7;
ll n,m,l;
string s,t;
ll d[200010],dp[1010][1010];
double w[1000],v[1000];
double box[200010];

ll func(){
  rep(i,0,s.sz)dp[i][0] = 0;
  rep(i,0,t.sz)dp[0][i] = 0;
  rep(i,0,s.sz){
    rep(j,0,t.sz){
      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]);
      }
    }
  }
  return dp[s.sz][t.sz];
}

int main(){
  cin >> n;
  rep(i,0,n){
    cin >> s >> t;
    print(func());
  }
  return 0;
}

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++: // -*- mode:c++; coding:utf-8; c-basic-offset:2; -*-
// ALDS1_10_C: Longest Common Subsequence

#include <algorithm>
#include <cstdio>
#include <cstring>

static unsigned int lcs(const char* x, const char* y)
{
  auto m = static_cast<int>(std::strlen(x));
  auto n = static_cast<int>(std::strlen(y));
  unsigned int c[m+1][n+1]; // extend -1

  for (auto i = 0; i < m+1; ++i) c[i][0] = 0u;
  for (auto j = 1; j < n+1; ++j) c[0][j] = 0u;

  for (auto i = 0; i < m; ++i) {
    for (auto j = 0; j < n; ++j) {
      c[i+1][j+1] = (x[i] == y[j])
        ? c[i][j] + 1
        : std::max(c[i+1][j], c[i][j+1]);
    }
  }
  return c[m][n];
}

int main()
{
  unsigned int q;
  std::scanf("%u", &q);
  const unsigned int MAX_LEN = 1000;
  char x[MAX_LEN+1], y[MAX_LEN+1];
  for (auto i = 0u; i < q; ++i) {
    std::scanf("%1000s", x);
    std::scanf("%1000s", y);
    auto l = lcs(x, y);
    std::printf("%u\n", l);
  }
}

// eof