Valid Parentheses

为了在运行中避免可能出现的危险，即当string emuStack为空，emuStack.begin()和emuStack.end()是什么。采取的策略是先将emuStack重置为非空，再进行其他操作，这样就永远不可能碰到底部。

#include<iostream>#include<string>using namespace std;class Solution {public:    bool isValid(string s) {    if(s.size() == 0)return true;string emuStack = "s";string::iterator iter1 = s.begin();string::iterator iter2 = emuStack.begin();for(; iter1 != s.end(); iter1++) {if(*iter1 == '}') {if(*iter2 == '{') {emuStack.erase(iter2);iter2 = emuStack.end() - 1;continue;}}if(*iter1 == ']') {if(*iter2 == '[') {emuStack.erase(iter2);iter2 = emuStack.end() - 1;continue;}}if(*iter1 == ')') {if(*iter2 == '(') {emuStack.erase(iter2);iter2 = emuStack.end() - 1;continue;}}if((*iter1 == '{') || (*iter1 == '}') || (*iter1 == '[') || (*iter1 == ']') || (*iter1 == '(') || (*iter1 == ')')) {emuStack += *iter1;iter2 = emuStack.end() - 1;}}//cout << emuStack << endl;if(emuStack.size() == 1)//cout << "valid" << endl;return true;else//cout << "no valid" << endl;return false;//getchar();//return 1;}};int main() {//string s = "a{b[c(d)e]f}g";string s = "]";Solution solution;cout << solution.isValid(s) << endl;getchar();return 1;}