020_有效的括号

简单

Java

class Solution {
    public boolean isValid(String s) {
        int[] stack = new int[s.length()];
        int index = 0;
        for(int i = 0;i < s.length();i++){
            char c = s.charAt(i);
            if(index == 0 && (c == ')' || c == ']' || c == '}')){
                return false;
            }
            if(c == '(' || c == '[' || c == '{'){
                stack[index] = s.charAt(i);
                index++;
            }else if(c == ')' && stack[index-1] == '(' || c == ']' && stack[index-1] == '[' || c == '}' && stack[index-1] == '{'){
                index--;
            }else{
                return false;
            }
        }
        if(index == 0){
            return true;
        }else {
            return false;
        }
    }
}

Python

class Solution:
    def isValid(self, s: str) -> bool:
        stack = deque()
        for i in s:
            if i == ')' and len(stack) > 0 and stack.pop() == '(': continue 
            elif i == ']' and len(stack) > 0 and stack.pop() == '[': continue
            elif i == '}' and len(stack) > 0 and stack.pop() == '{': continue
            elif i == '(' or i == '[' or i == '{': stack.append(i)
            else: return False
        return True if len(stack) == 0 else False