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

int main(){
  int n;
  char x[1001],y[1001];
  int dp[1002][1002];
  


  //load n;
  cin >>n;
  for(int i=0;i<n;i++){
    //initialize
    for(int i=0;i<1002;i++){
      for(int j=0;j<1002;j++){
	dp[i][j]=0; 
      }
    }
    //load string
    scanf("%s",x);
    scanf("%s",y);
    //dp
    for(int j=0;j<strlen(x);j++){
      for(int k=0;k<strlen(y);k++){
	if(x[j]==y[k]){
	  dp[j+1][k+1]=dp[j][k]+1;
	}

	else{
 
	  if(dp[j][k+1]>dp[j+1][k]){
	    dp[j+1][k+1]=dp[j][k+1];
	  }

	  else{
	    dp[j+1][k+1]=dp[j+1][k];
	  }
	}
      }
    }

    //print
    cout <<dp[strlen(x)][strlen(y)]<<endl;
  }



  return 0;
}

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


int main(){
    string str1,str2;
    int n, len1, len2;
    scanf("%d",&n);
    for(int i=1;i<=n;++i){
        cin>>str1>>str2;
        //scanf("%s",str1);
        //scanf("%s",str2);
        len1 = str1.size();
        len2 = str2.size();
        str1 = ' '+str1;
        str2 = ' '+str2;
        int c[len1+1][len2+1];
        for(int i=0;i<=len1;++i) c[i][0] = 0;
        for(int i=0;i<=len2;++i) c[0][i] = 0;
        for(int i=1;i<=len1;++i){
            for(int j=1;j<=len2;++j){
                if(str1[i]==str2[j]){
                    c[i][j] = c[i-1][j-1]+1;
                }
                else{
                    c[i][j] = max(c[i-1][j],c[i][j-1]);
                }
            }
        }
        printf("%d\n",c[len1][len2]);
    }
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
int dp[1010][1010];
int main(){
  int q;
  cin>>q;
  for(int cn=0;cn<q;cn++){
    string x,y;
    cin>>x>>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;
	dp[i][j]=max(dp[i-1][j],dp[i][j]);
	dp[i][j]=max(dp[i][j-1],dp[i][j]);
      }
    }
    cout<<dp[x.size()][y.size()]<<endl;
  }
  return 0;
}

C++: #include <iostream>
#include <string>
using namespace std;

int lcs(string X, string Y) {
  int dp[1000 + 1][1000 + 1];
  int max = 0;
  X = ' ' + X;
  Y = ' ' + Y;
  for (unsigned int i = 1; i <= X.size() - 1; i++)
    dp[i][0] = 0;

  for (unsigned int i = 1; i <= Y.size() - 1; i++)
    dp[0][i] = 0;
  for (unsigned int i = 1; i <= X.size() - 1; i++) {
    for (unsigned int j = 1; j <= Y.size() - 1; j++) {
      if (X[i] == Y[i])
	dp[i][j] = dp[i - 1][j - 1] + 1;
      else if (dp[i - 1][j] >= dp[i][j - 1])
	dp[i][j] = dp[i - 1][j];
      else
	dp[i][j] = dp[i][j - 1];

      max = (max < dp[i][j]) ? dp[i][j] : max;
    }
  }

  return max;
}

int main(int argc, char const *argv[]) {
  int N;
  cin >> N;

  for (int i = 0; i < N; i++) {
    string X, Y;
    cin >> X >> Y;

    cout << lcs(X, Y) << 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() - 1;
  int n1 = s1_.length() - 1;
  return getLCSlenOf(n0, n1);
}


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

  assert(-1 <= n0 && n0 < static_cast<int>(s0_.length()));
  assert(-1 <= n1 && n1 < static_cast<int>(s1_.length()));

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

  const int idx = getIndex(n0, n1);

  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 <cmath>
#include <vector>
#include <cstring>

constexpr int MAX = 1000;
char ls[MAX];
char rs[MAX];
int table[MAX + 1][MAX + 1];


void calc_lcs() {
    scanf("%s", ls);
    scanf("%s", rs);
    int l_len = int(std::strlen(ls));
    int r_len = int(std::strlen(rs));
    for (int i = 0; i < l_len; i++) {
        table[i][0] = 0;
    }
    for (int i = 0; i < r_len; i++) {
        table[0][i] = 0;
    }

    for (int l_i = 1; l_i < l_len + 1; l_i++) {
        for (int r_i = 1; r_i < r_len + 1; r_i++) {
            if (ls[l_i - 1] == rs[r_i - 1]) {
                table[l_i][r_i] = table[l_i - 1][r_i - 1] + 1;
            } else {
                table[l_i][r_i] = std::max(table[l_i][r_i - 1], table[l_i - 1][r_i]);
            }
        }
    }
    std::cout << table[l_len][r_len] << std::endl;
}

int main() {
    int N;
    scanf("%d", &N);
    for (int i = 0; i < N; i++) {
        calc_lcs();
    }
}