【原】LeetCode之Valid Parentheses

陳喻 2021-10-19

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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

用stack來(lái)實(shí)現(xiàn)，左邊的進(jìn)棧，如果是右邊的出棧，發(fā)現(xiàn)沒(méi)有或者不匹配就返回false

3、代碼實(shí)現(xiàn)

public class Solution {
    public boolean isValid(String s) {
        if (s == null || s.length() == 0) {
        return false;
        }
        char chars[] = s.toCharArray();
        Stack<Character> stack = new Stack<Character>();
        for (int i = 0; i < chars.length; ++i) {
        if (chars[i] == '(' || chars[i] == '{' || chars[i] == '[') {
        stack.add(chars[i]);
        } else {
        if (!stack.isEmpty()) {
        Character value = stack.pop();
        if (chars[i] == ')') {
        if (value != '(') 
        return false;
        }
        if (chars[i] == '}') {
        if (value != '{') 
        return false;
        }
        if (chars[i] == ']') {
        if (value != '[') 
        return false;
        }
        } else {
        return false;
        }
        }
        }
        return stack.isEmpty();
    }
}