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++: #pragma GCC optimize ("O3")

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <queue>
#include <set>
#include <algorithm>
#include <numeric>
#include <string>
using namespace std;

using QWORD  = uint64_t;
using SQWORD = int64_t;
using DWORD  = uint32_t;
using SDWORD = int32_t;
using WORD   = uint16_t;
using SWORD  = int16_t;
using BYTE   = uint8_t;
using SBYTE  = int8_t;
using DOUBLE = double;
using FLOAT  = float;

#define MIN_SDWORD (-2147483648)
#define MAX_SDWORD (2147483647)
#define MIN_SBYTE (-128)
#define MAX_SBYTE (127)

#define MIN_SQWORD (0x8000000000000000)
#define MAX_SQWORD (0x7FFFFFFFFFFFFFFF)

#define MAX_QWORD  (0xFFFFFFFFFFFFFFFF)
#define MAX_DWORD  (0xFFFFFFFF)
#define MAX_WORD   (0xFFFF)
#define MAX_BYTE   (0xFF)


#define ArrayLength(a)  (sizeof(a) / sizeof(a[0]))

static inline QWORD MAX(QWORD a, QWORD b) { return a > b ? a : b; }
static inline DWORD MAX(DWORD a, DWORD b) { return a > b ? a : b; }
static inline SDWORD MAX(SDWORD a, SDWORD b) { return a > b ? a : b; }
static inline QWORD MIN(QWORD a, QWORD b) { return a < b ? a : b; }
static inline DWORD MIN(DWORD a, DWORD b) { return a < b ? a : b; }
static inline SDWORD MIN(SDWORD a, SDWORD b) { return a < b ? a : b; }

#define BYTE_BITS   (8)
#define WORD_BITS   (16)
#define DWORD_BITS  (32)
#define QWORD_BITS  (64)

using M_BOOL = bool;
#define M_TRUE (true)
#define M_FALSE (false)
#define DIVISOR (1000000007)

static inline void inputString(char *pcStr)
{
    char *pcCur = pcStr;
    for (;;) {
        char c = getchar();
        if (('\n' == c) || (EOF == c)) {
            break;
        }
        *pcCur = c;
        pcCur++;
    }
    *pcCur = '\0';
}


static inline SQWORD inputSQWORD(void)
{
    SQWORD sqNumber = 0;
    SQWORD sqMultiplier = 1;
    M_BOOL bRead = M_FALSE;
    for (;;) {
        char c = getchar();
        if (!bRead) {
            if ('-' == c) {
                sqMultiplier = -1;
            }
        }
        if (('0' <= c) && (c <= '9')) {
            sqNumber *= 10LL;
            sqNumber += (SQWORD)(c - '0');
            bRead = M_TRUE;
        } else {
            if (bRead) {
                return sqNumber * sqMultiplier;
            }
        }
    }
}


static inline SDWORD inputSDWORD(void)
{
    SDWORD lNumber = 0;
    SDWORD lMultiplier = 1;
    M_BOOL bRead = M_FALSE;
    for (;;) {
        char c = getchar();
        if (!bRead) {
            if ('-' == c) {
                lMultiplier = -1;
            }
        }
        if (('0' <= c) && (c <= '9')) {
            lNumber *= 10;
            lNumber += (c - '0');
            bRead = M_TRUE;
        } else {
            if (bRead) {
                return lNumber * lMultiplier;
            }
        }
    }
}

static inline DOUBLE inputFP(void)
{
    DOUBLE dInt = 0.0;
    DOUBLE dFrac = 0.0;
    DOUBLE dMultiplier = 1.0;
    DWORD dwFpCnt = 0;
    DOUBLE *pdCur = &dInt;
    M_BOOL bRead = M_FALSE;
    for (;;) {
        char c = getchar();
        if (!bRead) {
            if ('-' == c) {
                dMultiplier = -1;
            }
        }
        if ('.' == c) {
            pdCur = &dFrac;
        } else if (('0' <= c) && (c <= '9')) {
            (*pdCur) *= 10;
            (*pdCur) += (DOUBLE)(c - '0');
            bRead = M_TRUE;
            if (pdCur == &dFrac) {
                dwFpCnt++;
            }
        } else {
            if (bRead) {
                return dMultiplier * (dInt + dFrac / (pow((DOUBLE)10.0 , (DOUBLE)dwFpCnt)));
            }
        }
    }
}

#define MAX_STR_LEN (1000)
static void getLongestCommonSubsequence(
    const string &strS1,
    const string &strS2)
{
    /* dp[i+1][j+1]: S1のi文字目, S2のj文字目までで一致する最長の文字数 */
    /**
     *  初期化をさぼるため、dptbl のインデックスをひとつずらしている
     */
    static SDWORD alDpTbl[MAX_STR_LEN + 1];
    static SDWORD alNextDpTbl[MAX_STR_LEN + 1];
    memset(alDpTbl, 0, sizeof(alDpTbl));

    for (SDWORD lIdxS1 = 0; lIdxS1 < strS1.size(); lIdxS1++) {
        alNextDpTbl[0] = 0;
        for (SDWORD lIdxS2 = 0; lIdxS2 < strS2.size(); lIdxS2++) {
            if (strS1[lIdxS1] == strS2[lIdxS2]) {
                alNextDpTbl[lIdxS2+1] = alDpTbl[lIdxS2] + 1;
            } else {
                alNextDpTbl[lIdxS2+1] = max(alDpTbl[lIdxS2+1],
                                                    alNextDpTbl[lIdxS2]);
            }
        }
        memcpy(alDpTbl, alNextDpTbl, sizeof(alDpTbl));
    }

    printf("%d\n", alDpTbl[strS2.size()]);
}

int main()
{
    SDWORD  lNumDataSet = inputSDWORD();
    char acStr1[MAX_STR_LEN + 1];
    char acStr2[MAX_STR_LEN + 1];

    for (SDWORD lIdx = 0; lIdx < lNumDataSet; lIdx++) {
        inputString(acStr1);
        inputString(acStr2);


        string strS1(acStr1);
        string strS2(acStr2);
        getLongestCommonSubsequence(strS1, strS2);
    }

    return 0;
}

C++: #include <iostream>
#include <string>
#include <algorithm>
#define int long long
using namespace std;

signed main() {
  int n;
  cin >> n;
  for (int c = 0; c < n; c++) {
    string x, y;
    cin >> x >> y;

    int dp[x.size() + 1][y.size() + 1];
    for (int i = 0; i < x.size() + 1; i++) {
      dp[i][0] = 0;
    }

    for (int j = 0; j < y.size() + 1; j++) {
      dp[0][j] = 0;
    }
      
    for (int i = 1; i < x.size() + 1; i++) {
      for (int j = 1; j < y.size() + 1; 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]);
	}
      }
    }

    cout << dp[x.size()][y.size()] << endl;
  }

  return 0;
}

C++: #include <iostream>
#include <string>
#include <algorithm>
using namespace std;
 
static const long N = 1000;
 
long lcs(string X, string Y){
    long c[N + 1][N + 1];
    long m = X.size();
    long n = Y.size();
    long maxl = 0;
    X = ' ' + X;
    Y = ' ' + Y;
    for (long i = 1; i <= m; i++) c[i][0] = 0;
    for (long j = 1; j <= n; j++) c[0][j] = 0;
 
    for (long i = 1; i <= m; i++){
        for (long 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 = c[i][j];
        }
    }
 
    return maxl;
}
 
int main(){
    string s1, s2;
    long n;
    cin >> n;
    for (long i = 0; i < n; i++){
        cin >> s1 >> s2;
        cout << lcs(s1, s2) << endl;
    }
    return 0;
}