#20 Valid Parentheses

题目链接：https://leetcode.com/problems/valid-parentheses/

Given a string containing just the characters '(', ')','{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

typedef struct StackRecord {    //不考虑溢栈实现简单的堆栈char ch[100];int top;}*Stack;bool isEmpty(Stack stack) {if (stack->top >= 0)return false;return true;}Stack init() {Stack stack = (Stack)malloc(sizeof(struct StackRecord));stack->top = -1;return stack;}void push(char ch, Stack stack) {stack->ch[++stack->top] = ch;}char top(Stack stack) {     //返回栈顶元素，空栈时返回'\0'    if(!isEmpty(stack))    return stack->ch[stack->top];return 0;}void pop(Stack stack) {--stack->top;}bool isValid(char* s) {Stack stack = init();while (*s) {switch (*s) {case '(':       //左括号入栈case '[':case '{':push(*s, stack);break;case ')':      //右括号，查看栈顶是否为对应左括号。不是返回false；否则出栈if (top(stack) != '(')return false;pop(stack);break;case ']':if (top(stack) != '[')return false;pop(stack);break;case '}':if (top(stack) != '{')return false;pop(stack);break;default:return false;}++s;}if (!isEmpty(stack))        //栈内不空说明有多余左括号return false;return true;}