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 <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++){
			if (X[i] == Y[j]) {
				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 <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++: #include <stdio.h>
#include <stdint.h>
#include <iostream>
#include <fstream>
#include <cassert>
#include <climits>
#include <vector>
#include <memory>
using namespace std;

#define DEBUG (0)

#if DEBUG
#define DPRINTF(...) do { \
    printf("D(L%d) %s: ", __LINE__, __func__); \
    printf(__VA_ARGS__); \
  } while (false)
#else
#define DPRINTF(...)
#endif // DEBUG


class LongestCommonSubsequence {
public:
  LongestCommonSubsequence(string s0, string s1) :
    s0_(s0),
    s1_(s1)
    {
      size_ = s0_.length() * s1_.length();
      pLongest_ = new int [size_];
      for (int i = 0; i < size_; i++)
        pLongest_[i] = kInvalid;
    }

  ~LongestCommonSubsequence()
  {
    if (pLongest_)
      free(pLongest_);
  }

  int getLCSlen();
  void printLength();

  const int kInvalid = -1;

private:
  string s0_;
  string s1_;
  int *pLongest_;
  int size_;

  int getIndex(int x, int y);
  int getLCSlenOf(int n0, int n1);
};

/*********************************
Input:
  x[0], x[1], x[2], ..., x[n-1]
  y[0], y[1], y[2], ..., y[m-1]

Algorithm:
  if x[n-1] == y[m-1]
    LCS(n-1, m-1) = LCS(n-2,m-2) + 1

  if x[n-1] != y[m-1]
    LCS(n-1, m-1) = max(LCS(n-2, m-1), LCS(n-1, m-2))

  LCS(0, *) = LCS(*, 0) = 0;

  a b c b d a b
  b d c a b a
*********************************/

int LongestCommonSubsequence::getLCSlen()
{
  int n0 = s0_.length();
  int n1 = s1_.length();
  return getLCSlenOf(n0, n1);
}


int LongestCommonSubsequence::getLCSlenOf(int n0, int n1)
{
  DPRINTF("n0 %d  n1 %d\n", n0, n1);

  assert(0 <= n0 && n0 <= s0_.length());
  assert(0 <= n1 && n1 <= s1_.length());

  if (n0 == 0 || n1 == 0)
    return 0;

  const int idx = getIndex(n0 - 1, n1 - 1);

  if (pLongest_[idx] != kInvalid)
    return pLongest_[idx];

  if (s0_[n0] == s1_[n1])
    pLongest_[idx] = getLCSlenOf(n0 - 1, n1 - 1) + 1;
  else
    pLongest_[idx] = max(getLCSlenOf(n0 - 1, n1), getLCSlenOf(n0, n1 - 1));

  return pLongest_[idx];
}


int LongestCommonSubsequence::getIndex(int x, int y)
{
  return y * s0_.length() + x;
}


void LongestCommonSubsequence::printLength()
{
  for (int i = 0; i < s0_.length(); i++)
    for (int j = 0; j < s1_.length(); j++)
      DPRINTF("pLongest_[%d][%d] %d\n", i, j, pLongest_[getIndex(i, j)]);
}


int main()
{
  int numOfPair;
  cin >> numOfPair; cin.ignore();

  DPRINTF("num of pair %d\n", numOfPair);

  for (int i = 0; i < numOfPair; i++)
  {
    string str0, str1;
    cin >> str0 >> str1; cin.ignore();

    DPRINTF("str0 %s  str1 %s\n", str0.c_str(), str1.c_str());

    LongestCommonSubsequence lcs(str0, str1);
    cout << lcs.getLCSlen() << endl;

#if (1) && DEBUG
    lcs.printLength();
#endif
  }

  return 0;
}

C++: #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=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() {
  std::ios::sync_with_stdio(false);
  cout.tie(0);
  cin.tie(0);
  int n;
  cin>>n;
  string s1,s2;
  for (int i=0; i<n; i++) {
    cin>>s1>>s2;
    cout<<lcs(s1,s2)<<endl;
  }
  return 0;
}