Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	Q := sc.nextInt()
	for q := 0; q < Q; q++ {
		X, Y := sc.nextStr(), sc.nextStr()
		xLen, yLen := len(X), len(Y)
		dp := make([][]int, xLen+1)
		for i := 0; i <= xLen; i++ {
			dp[i] = make([]int, yLen+1)
		}
		for x := 0; x <= xLen; x++ {
			for y := 0; y <= yLen; y++ {
				if x == 0 || y == 0 {
					dp[x][y] = 0
				} else if X[x-1] == Y[y-1] {
					dp[x][y] = dp[x-1][y-1] + 1
				} else {
					dp[x][y] = max(dp[x-1][y], dp[x][y-1])
				}
			}
		}
		fmt.Fprintln(wtr, dp[xLen][yLen])
	}

	wtr.Flush()
}

C++: #include <algorithm>
#include <iostream>
#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 = 0; 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;
  }
}

C++: #include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;
int LCS(const char* a,const char* b)
{
    int m=strlen(a); int n=strlen(b); //i???????¬????a????????????j???????¬????b?????????
    int c[m+1][n+1]; //c??°???????????¨?????°???????¬????a??????i??????????¬????b??????j????????´???LCS
    for(int i=0;i<=m;i++) c[i][0]=0;
    for(int i=0;i<=n;i++) c[0][i]=0;
    for(int i=0;i<m;i++)
        for(int j=0;j<n;j++)
        {
            if(a[i]==b[j]) c[i+1][j+1]=c[i][j]+1;
            else
            {
                c[i+1][j+1]=max(c[i][j+1],c[i+1][j]);
            }
        }
    return c[m][n];

}
int main()
{
    char *a=new char[1001];
    char *b=new char[1001];
    int q;
    while(cin>>q)
    {
        for(int i=0;i<q;i++)
        {
            cin>>a>>b;
            cout<<LCS(a,b)<<endl;
        }
    }
}

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 = 0; 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 <cstdio>
#include <cstdlib>
#include <string>
#include <iostream>

using namespace std;
static const int N=1000;
int lcs(string X, string Y){
    int m=X.size();
    int n=Y.size();
    int c[N+1][N+1];
    int maxl=0;
    X=' '+X;
    Y=' '+Y;
    int i,j;
    for(i=1;i<=m;i++)c[i][0]=0;
    for(j=1;j<=n;j++)c[0][j]=0;

    for(i=1;i<=m;i++){
        for(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][j-1],c[i-1][j]);
            }
            maxl=max(maxl,c[i][j]);
        }
    }
    return maxl;
}
int main()
{
    int n;
    string s1,s2;
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>s1>>s2;
        cout<<lcs(s1,s2)<<endl;
    }

    return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstdlib>
#include <string>
#include <iostream>
#include <queue>

using namespace std;

const char *X, *Y;
int X_length, Y_length;

int table_lcs[1001][1001];

int lcs(int x_begin, int y_begin) {
	int i, j, to;
	int max = 0;
	int v_lcs;
	bool alreadySeenTable[256];
	if (table_lcs[x_begin][y_begin] != -1) {
		return table_lcs[x_begin][y_begin];
	}
	
	for (i = 0; i < 256; i++) {
		alreadySeenTable[i] = false;
	}
	i = x_begin;
	to = Y_length-1;
	while(i <= X_length-1) {
		j = y_begin;
		if (alreadySeenTable[X[i]] == true) {
			i++;
			continue;
		}
		bool found = false;
		while (j <= to) {
			if (X[i] == Y[j]) {
				v_lcs = lcs(i + 1, j + 1) + 1;
				if (v_lcs > max) {
					max = v_lcs;
				}
				found = true;
				break;
			}
			else {
				j++;
			}
		}
		if (found == false) {
			alreadySeenTable[X[i]] = true;
			i++;
		}
		else {
			alreadySeenTable[X[i]] = true;
			i++;
			to = j - 1;
		}
	}
	return table_lcs[x_begin][y_begin] = max;
}

int lcs2(int x_begin, int y_begin) {
	int i, j, to;
	int max = 0;
	int v_lcs;
	if (table_lcs[x_begin][y_begin] != -1) {
		return table_lcs[x_begin][y_begin];
	}

	i = x_begin;
	to = Y_length - 1;
	while (i <= X_length - 1) {
		j = y_begin;
		bool found = false;
		while (j <= to) {
			if (X[i] == Y[j]) {
				v_lcs = lcs(i + 1, j + 1) + 1;
				if (v_lcs > max) {
					max = v_lcs;
				}
				found = true;
				break;
			}
			else {
				j++;
			}
		}
		if (found == false) {
			i++;
		}
		else {
			i++;
			to = j - 1;
		}
	}
	return table_lcs[x_begin][y_begin] = max;
}

int main() {

	int N;
	cin >> N;
	string stringX, stringY;

	for (int i = 1; i <= N; i++) {
		for (int i = 0; i < 1001; i++) {
			for (int j = 0; j < 1001; j++) {
				table_lcs[i][j] = -1;
			}
		}
		cin >> stringX >> stringY;
		X = stringX.c_str();
		X_length = stringX.size();
		Y = stringY.c_str();
		Y_length = stringY.size();
		printf("%d\n", lcs2(0, 0));
	}
	return 0;
}

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

int dp[1010][1010];

int main()
{
  int q;
  string x,y;

  cin >> q;

  for(int t = 0;t < q;t++){
    cin >> x;
    cin >> y;

    memset(dp, 0, sizeof(dp));
    
    for(int i = 1;i <= x.size();i++){
      for(int j = 1;j <= y.size();j++){

	if(x[i-1] == y[j-1]){
	  dp[i][j] = dp[i-1][j-1]+1;
	}
	else if(dp[i-1][j] <= dp[i][j-1]){
	  dp[i][j] = dp[i][j-1];
	}
	else{
	  dp[i][j] = dp[i-1][j];
	}
      }
    }
    cout << dp[x.size()][y.size()] << endl;
  }
  return 0;
}