递归-求字符串的子序列

概念：

// 字符串 abcdef
// 字符串的子串：abcde, abc, ab, a, bcdef, bcde ......
// 字符串的子序列：acd, adf, acdf, bef, bf ......

代码：

#include <iostream>
#include <string>
#include <algorithm>
 
using namespace std;
 
// 字符串 abcdef 
// 字符串的子串：abcde, abc, ab, a, bcdef, bcde ......
// 字符串的子序列：acd, adf, acdf, bef, bf ......
 
int F(string _mainstr, string _substr)
{
    if(_mainstr.length() == 0 || _substr.length() == 0)
        return 0;
     
    if(_mainstr.at(0) == _substr.at(0))
        return F(_mainstr.substr(1), _substr.substr(1)) + 1;
    else
        return max(F(_mainstr.substr(1), _substr), F(_mainstr, _substr.substr(1)));
}
 
int main()
{
    string mainstr = "abcdef";
    string substr = "xbdcnefe";
     
    //cout << mainstr.substr(1, mainstr.length()); 
     
    cout << F(mainstr, substr);
     
    return 0;
}