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] = 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++: // https://ei1333.github.io/luzhiled/
// http://beet-aizu.hatenablog.com/entry/2017/01/04/113233
// http://www.prefield.com/algorithm/
#include <bits/stdc++.h>
constexpr char bn = '\n';
using namespace std;
using ll = long long;
using ld = long double;
using vl = vector<ll>;
using vd = vector<ld>;
using vs = vector<string>;
using vb = vector<bool>;
using vvl = vector<vector<ll>>;
using vvd = vector<vector<ld>>;
using vvs = vector<vector<string>>;
using vvb = vector<vector<bool>>;
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
template<class T> using vc = vector<T>;
template<class T> using vvc = vector<vector<T>>;
using Graph = vector<vector<ll>>;
const ll INF = 1LL << 60;
void init() {cin.tie(0);ios::sync_with_stdio(false);cout << fixed << setprecision(15);}
const ll tl= 1000000007;
#define REP(i, n) for (ll i = 0; i < n; i++)
#define REREP(i, n) for (ll i = n; i >= 0; i--)
#define FOR(i, a, n) for (ll i = a; i < n; i++)
#define REFOR(i, n, a) for (ll i = n; i >= a; i--)
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() ) //被り削除
#define debug cout << "line : " << __LINE__ << " debug" << endl;
#define ini(...) int __VA_ARGS__; in(__VA_ARGS__)
#define inl(...) long long __VA_ARGS__; in(__VA_ARGS__)
#define ind(...) long double __VA_ARGS__; in(__VA_ARGS__)
#define ins(...) string __VA_ARGS__; in(__VA_ARGS__)
#define inc(...) char __VA_ARGS__; in(__VA_ARGS__)
void in(){} template <typename T,class... U> void in(T &t,U &...u){ cin >> t; in(u...);}
void out(){cout << endl;} template <typename T,class... U> void out(const T &t,const U &...u){ cout << t; if(sizeof...(u)) cout << " "; out(u...);}
template<typename T>void die(T x){out(x); exit(0);}
#define in1(A) REP(i,A.size()) in(A[i]);
#define in2(A,B) REP(i,A.size()) in(A[i],B[i]);
#define in3(s,t,u) REP(i,sz(s)){in(s[i] , t[i] , u[i]);}
#define in4(s,t,u,v) REP(i,sz(s)){in(s[i] , t[i] , u[i] , v[i]);}
#define each(x,v) for(auto& x : v)
#define all(v) (v).begin(),(v).end()
#define sz(v) ((int)(v).size())
struct Point{ ld x,y; };
ld dist(Point a, Point b){return sqrt(abs(a.x-b.x)*abs(a.x-b.x)+abs(a.y-b.y)*abs(a.y-b.y));} // ２点間の距離 
ll gcd(ll a, ll b) { return b != 0 ? gcd(b, a % b) : a; }
ll lcm(ll a,ll b){ return a / gcd(a,b) * b;} 
ll fact(ll n){ if(n < 2) return 1; return (n * fact(n-1))%tl; } //階乗
inline ll updiv(ll a,ll b){ return (a + b - 1) / b; } //切り上げ
template<typename T,typename U>ll ceil(T a,U b){return (a + b - 1) / b;}
template <class A, class B> inline bool chmax(A &a, const B &b) { return b > a && (a = b, true); }
template <class A, class B> inline bool chmin(A &a, const B &b) { return b < a && (a = b, true); }
//-------------------------------------------------------------------------------------------------
ll lcs(string x, string y){
    ll r= x.size(),c= y.size();
    vvl A(r, vl(c,0));
    REP(i,r){ // xをiもじめまで見る
        REP(j,c){ //yをj
            // 最初やること xとyそれぞれ1文字目が含まれているか
            // 含まれていたらそれ以降1
            if(!(i*j)){
                if(i) A[i][0]= A[i-1][0];
                if(j) A[0][j]= A[0][j-1];
                if(x[i]==y[j]) A[i][j]=1;
            }else{
                if(x[i]!=y[j]){
                    //間違いなら左か上から大きい方
                    A[i][j]= max(A[i-1][j],A[i][j-1]);
                }else{
                    //合っていたなら左上+1
                    // 左や上から取ることはできない(すでにその文字が使われているため)
                    A[i][j]= A[i-1][j-1]+1;
                }
            }
        }
    }

    return A[r-1][c-1];
}
int main(){
    init();
    inl(n); 
    vl ans;
    while(n--){
        ins(x,y);
        ans.pb(lcs(x,y));
    }
    each(x,ans) out(x);
}

C++: #include <iostream>
#include <vector>

using ll = long long;
using namespace std;

/* initialize */
int lcs(string A, string B){
    int m = A.length(), n = B.length();
    int c[m+1][n+1];
    for (int i = 0; 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 (A[i]==B[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];
};
/* main */
int main() {
    int n;
    cin >> n;
    string s1, s2;
    for (int i = 0; i < n; ++i) {
        cin >> s1 >> s2;
        int s = lcs(s1, s2);
        cout << s << "\n";
    }
    return 0;
}

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

using namespace std;

int dp[1100][1100];

void solve()
{
	string s1,s2;
	cin>>s1>>s2;
	memset(dp,0,sizeof(dp));
	for(int i=0;i<s1.length();i++)
		for(int j=0;j<s2.length();j++)
			dp[i+1][j+1]=(s1[i]==s2[j]?dp[i][j]+1:max(dp[i+1][j],dp[i][j+1]));
	printf("%d\n",dp[s1.length()][s2.length()]);
}

int main()
{
	int n;
	scanf("%d",&n);
	while(n--)
		solve();
	return 0;
}

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

#define REP(i, n) for(int i = 0; i < n; i++)
#define REPR(i, n) for(int i = n; i >= 0; i--)
#define FOR(i, m, n) for(int i = m; i < n; i++)
#define ALL(obj) (obj).begin(), (obj).end()
#define INF 1e9
typedef long long ll;


int main() {
    int q;
    cin >> q;
    REP(k,q){
        string X,Y;
        cin >> X;
        cin >> Y;
        int m,n;
        m = X.length();
        n = Y.length();

        vector<vector<int>> dp(m+1, vector<int>(n+1,0));

        REP(i,m){
            REP(j,n){
                if(X[i] == Y[j]){
                    dp[i+1][j+1] = max({dp[i+1][j+1], dp[i][j]+1});
                }
                dp[i+1][j+1] = max({dp[i+1][j+1], dp[i+1][j], dp[i][j+1]});
            }
        }
        cout << dp[m][n] << endl;
    }
    return 0;
}