Game with string CodeForce#1104B 栈、串

题目链接：Game with string

题目原文

Two people are playing a game with a string 𝑠s, consisting of lowercase latin letters.

On a player's turn, he should choose two consecutive equal letters in the string and delete them.

For example, if the string is equal to "xaax" than there is only one possible turn: delete "aa", so the string will become "xx". A player not able to make a turn loses.

Your task is to determine which player will win if both play optimally.

思路

很显然，假设可以删掉的'xx'的个数是奇数则先手玩家胜，若为偶数则后手玩家胜。

所以问题转化为求解s中可以删掉的xx'的个数。如果用模拟的话，估计会超时。遇到这种部分回文的序列，用栈来处理就方便很多了。把字符串s里的字符依次入栈，如果s[i]和栈顶元素相同，就出栈，同时ans++，最后判断ans的奇偶性即可。

题解

#include <iostream>
#include <cstring>
#include <stack>

using namespace std;

stack<char> s;
string str;

int main(int argc, char const *argv[])
{
    cin >> str;
    int ans = 0;
    for(int i = 0; i < str.length(); i++)
    {
        if(!s.empty() && str[i] == s.top())
        {
            ans++;
            s.pop();
        }
        else
        {
            s.push(str[i]);
        }
    }
    if(ans % 2 == 0)
    {
        cout << "No" << endl;
    }
    else
    {
        cout << "Yes" << endl;
    }
    return 0;
}