Sword To Offer 021 - 栈的压入、弹出序列

class Solution {
public:
    bool IsPopOrder(const vector<int>& pushV, const vector<int>& popV) {
        stack<int> _stack;
        int _pushIndex = 0;
        for (int i : popV) {
            while(_stack.empty() || _stack.top() != i) {
                _stack.push(pushV[_pushIndex++]);
                if(_pushIndex > pushV.size()) {
                    return false;
                }
            }
            _stack.pop();
        }
        return _stack.empty();
    }
};