[leetcode 20] Valid Parentheses

標籤：

1 題目

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.

 

2 思路

這題是真心比較簡單了，一個棧就可以解決了。需要主要empty的情況。

 

3 代碼：

    public boolean isValid(String s) {        Stack<Character> stack = new Stack<Character>();        for(Character ch : s.toCharArray()){            switch (ch) {            case ‘(‘:             case ‘[‘:            case ‘{‘: stack.push(ch);                break;                        case ‘)‘:            if(stack.empty() || stack.peek() != ‘(‘) {                return false;            }else{                stack.pop();              }             break;            case ‘}‘:            if(stack.empty() || stack.peek() != ‘{‘) {                return false;            }else{                stack.pop();              }             break;                        case ‘]‘:            if(stack.empty() || stack.peek() != ‘[‘) {                return false;            }else{                stack.pop();              }             break;            default: return false;            }        }       return stack.empty();    }

 

[leetcode 20] Valid Parentheses