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 <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();
    }
}