30-Day Leetcoding Challenge Day16

解法一：正反各遍历一次。正向遍历只要保证( 加 *的数量大于)。反向遍历保证* 加 )的数量大于(。

JAVA

class Solution {
    public boolean checkValidString(String s) {
        int left = 0;
        int right = 0;
        for(int i = 0; i < s.length(); i++){
            if(s.charAt(i) == ')'){
                left--;
            }
            else{
                left++;
            }
            if(left < 0)return false;
        }
        for(int i = s.length()-1; i >= 0; i--){
            if(s.charAt(i) == '('){
                right--;
            }
            else{
                right++;
            }
            if(right < 0)return false;
        }
        return true;
    }
}

Python3

class Solution:
    def checkValidString(self, s: str) -> bool:
        left = 0
        right = 0
        for i in range(len(s)):
            if s[i] == ')':
                left -= 1
            else:
                left += 1
            if left < 0:
                return False
        if left == 0 :
            return True #bug 应对这种输入'('
        for j in range(len(s)-1,-1,-1):
            if s[j] == '(':
                right -= 1
            else:
                right += 1
            if right < 0:
                return False
        return True