博客：
 https://www.cnblogs.com/sasuke-/p/5396843.html

模板

#include<iostream>
#include<cstdio>
#include<cstring>
#define MAXN 1010
using namespace std;
int c[MAXN][MAXN];//保存各个公共子序列的长度
int b[MAXN][MAXN];//记录来源
char s1[MAXN], s2[MAXN];
int len1, len2;
void LCSL()
{
 for (int i = 1; i <= len1; ++i)//控制s1序列
 {
  for (int j = 1; j <= len2; ++j)//控制s2
  {
   if (s1[i - 1] == s2[j - 1])
   {//如果字符相同最长公共子序列+1
    c[i][j] = c[i - 1][j - 1] + 1;
    b[i][j] = 1;  //表示来源自斜对角
   }
   else
   {
    if (c[i][j - 1] >= c[i - 1][j])
    {
     c[i][j] = c[i][j - 1];//继承最相邻原有的最大长度
     b[i][j] = 2;//记录来源自左边
    }
    else
    {
     c[i][j] = c[i - 1][j];
     b[i][j] = 3;
    }
   }
  }
 }
}
void print(int i, int j)
{
 if (i == 0 || j == 0)return;
 if (b[i][j] == 1)
 {
  print(i - 1, j - 1);
  cout << s1[i - 1];
 }
 else if (b[i][j]==2)
 {
  print(i, j - 1);
 }
 else
 {
  print(i - 1, j);
 }
}
int main()
{
 cout << "输入s1:" << endl;
 cin >> s1;
 cout << "输入s2:" << endl;
 cin >> s2;
 len1 = strlen(s1);
 len2 = strlen(s2);
 LCSL();
 cout << "s1与s2的最长公共子序列为" << c[len1][len2] << endl;
 print(len1, len2);
 printf("\n");
}