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<vector>
#include<string>
#define NIL -1
using namespace std;

int count(const string& X, int i, const string Y, int j,
          vector<vector<int> >& MEMO){
    if (i >= X.size() || j >= Y.size()) return 0;
    if (MEMO[i][j] != NIL) return MEMO[i][j];
    int next_Y = count(X, i    , Y, j + 1, MEMO);
    int next_X = count(X, i + 1, Y, j    , MEMO);
    int max_ = max(next_Y, next_X);
    int j_tmp = j;
    while (X[i] != Y[j_tmp]) {
        j_tmp++;
        if (j_tmp >= Y.size()) return max_;
    }
    int saiyou = count(X, i + 1, Y, j_tmp + 1, MEMO) + 1;
    if (max_ < saiyou) max_ = saiyou;
    return MEMO[i][j] = max_;
}

int main(){
    int q;
    cin >> q;
    for (int i = 0; i < q; i++) {
        string X, Y;
        cin >> X >> Y;
        vector<vector<int> > MEMO(X.size(), vector<int>(Y.size(), NIL));
        cout << count(X, 0, Y, 0, MEMO) << endl;
    }
    return 0;
}

C++: /*
** Longest Common Subsequence
*/

# include <cstdio>
# include <cstring>
# include <algorithm>
using namespace std;

const int MAX = 1000 + 5;

char s1[MAX], s2[MAX];
int c[MAX][MAX];

int lcs() {
    int m = strlen(s1);
    int n = strlen(s2);
    c[0][0] = 0;
    int maxl = 0;
    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 if (c[i-1][j] >= c[i][j-1]) {
                c[i][j] = c[i - 1][j];
            }
            else {
                c[i][j] = c[i][j - 1];
            }
            maxl = max(maxl, c[i][j]);
        }
    }

    return maxl;
}

void solve() {
    int n;
    scanf("%d", &n);
    while (n--) {
        scanf("%s %s", s1, s2);
        printf("%d\n", lcs());
    }
}

int main() {
    // freopen("infile", "r", stdin);
    // freopen("outfile", "w", stdout);
    solve();
    return 0;
}

C++: #include <iostream>

//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <tuple>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s)
{
    int v;
    istringstream sin(s);
    sin >> v;
    return v;
}
template <class T>
inline string toString(T x)
{
    ostringstream sout;
    sout << x;
    return sout.str();
}

//math
//-------------------------------------------
template <class T>
inline T sqr(T x) { return x * x; }

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<long long> VL;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

//container util
//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i, c) for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())

//repetition
//------------------------------------------
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI = acos(-1.0);

//clear memory
#define CLR(a) memset((a), 0, sizeof(a))

//debug
// #define dump(x) cerr << #x << " = " << (x) << endl;
// #define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" \
//                       << " " << __FILE__ << endl;

class LCS_Solver
{
    vector<VL> vl;
    string &s1;
    string &s2;

public:
    LCS_Solver(size_t s, string &s1, string &s2)
        : vl(s, VL(s, -1)), s1(s1), s2(s2)
    {
        vl[0][0] = 0;
        REP(i, s)
        {
            vl[0][i] = 0;
            vl[i][0] = 0;
        }
    }

    LL solve_memoize(int s1n, int s2m);
    LL solve_dp(int s1n, int s2m) const;
};

LL LCS_Solver::solve_memoize(int s1n, int s2m)
{
    // cout << s1n << ", " << s2m << endl;
    if (vl[s1n][s2m] >= 0)
    {
        return vl[s1n][s2m];
    }
    else
    {
        LL ans;
        if (s1[s1n - 1] == s2[s2m - 1])
        {
            ans =
                solve_memoize(s1n - 1, s2m - 1) + 1;
            vl[s1n][s2m] = ans;
            return ans;
        }
        else
        {
            ans = max(
                solve_memoize(s1n - 1, s2m),
                solve_memoize(s1n, s2m - 1));
            vl[s1n][s2m] = ans;
            return ans;
        }
    }
}

const size_t MAX_SIZE = 2000;

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

    LL ans;
    REP(_, n)
    {
        string s1, s2;
        cin >> s1;
        cin >> s2;
        // cout << s1.size() << " " << s2.size() << endl;

        ans = LCS_Solver(MAX_SIZE, s1, s2)
                  .solve_memoize(s1.size(), s2.size());
        cout << ans << endl;
    }
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define  all(x) (x).begin(),(x).end()
typedef long long ll;

int c[1005][1005];

int lcs(string s1, string s2){
    int n = s1.size();
    int m = s2.size();
    s1 = " " + s1;
    s2 = " " + s2;
    for(int i = 0; i <= n; i++) c[i][0] = 0;
    for(int i = 0; i <= n; i++) c[0][i] = 0;

    int ans = 0;
    for (int i1 = 1; i1 <= n; i1++){
        for(int i2 = 1; i2 <= m; i2++){
            if(s1[i1] == s2[i2]){
                c[i1][i2] = c[i1-1][i2-1] + 1;
            }else{
                c[i1][i2] = max(c[i1-1][i2], c[i1][i2-1]);
            }
        }
        ans = max(ans, c[i1][m]);
    }
    return ans;
}

int main(){
    int q;
    cin >> q;
    vector<int> ans(q);
    for(int i = 0; i < q; i++){
        string s1, s2;
        cin >> s1 >> s2;
        ans[i] = lcs(s1, s2);
    }
    rep(i,q) cout << ans[i] << endl;
    return 0;
}