cf D. Alternating Current

http://codeforces.com/contest/344/problem/D

#include <cstdio>
#include <cstring>
#include <stack>
#include <algorithm>
using namespace std;

char str[100001];
int main()
{
    stack<char>q;
    scanf("%s",str);
    int k=strlen(str);
    for(int i=0; i<k; i++)
    {
        if(q.empty())
        {
            q.push(str[i]);
        }
        else if(str[i]==q.top())
        {
            q.pop();
        }
        else if(str[i]!=q.top())
        {
            q.push(str[i]);
        }
    }
    if(!q.empty()) printf("No\n");
    else printf("Yes\n");
    return 0;
}