https://www.nowcoder.com/practice/8d3643ec29654cf8908b5cf3a0479fd5?tpId=308&tqId=40462&ru=/exam/oj

把string当栈用，扫一遍就可以了，时间复杂度O(n)

#include <iostream>
#include <string>
using namespace std;int main() {string s;cin >> s;int n = s.size();string st;for (int i = 0; i < n; ++i) {if (st.empty() || st.back() != s[i]) {st.push_back(s[i]);} else {st.pop_back();}}if (st.size() == 0) cout << 0;else cout << st;return 0;
}