[LeetCode-interview algorithm classic-Java implementation] [020-Valid Parentheses (bracket verification)],-javaparentheses

[LeetCode-interview algorithm classic-Java implementation] [020-Valid Parentheses (bracket verification)],-javaparentheses
[020-Valid Parentheses (bracket verification )][LeetCode-interview algorithm classic-Java implementation] [directory indexes for all questions]Original question

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.

Theme

Specify a string that only contains (',') ',' {','} ',' [', and'] 'to verify whether the string is valid. Parentheses must be paired and in the correct order.

Solutions

Use a stack to process the input parenthesis string. If the left bracket is used, it is written into the stack. If the right bracket is used, it is associated with the top element of the stack to check whether a pair of parentheses is formed, and process the parentheses of the next input. If they do not match, the result is returned directly.

Code Implementation

import java.util.*;public class Solution {    public boolean isValid(String s) {        Deque<Character> stack = new LinkedList<>();        int index = 0;        Character top;        while (index < s.length()) {            Character c = s.charAt(index);            switch (c) {                case '(':                case '[':                case '{':                    stack.addFirst(c);                    break;                case ')':                    if (stack.isEmpty()) {                        return false;                    }                    top = stack.getFirst();                    if (top == '(') {                        stack.removeFirst();                    } else if (top == '[' || top == '{') {                        return false;                    } else {                        stack.addFirst(c);                    }                    break;                case ']':                    if (stack.isEmpty()) {                        return false;                    }                    top = stack.getFirst();                    if (top == '[') {                        stack.removeFirst();                    } else if (top == '(' || top == '{') {                        return false;                    } else {                        stack.addFirst(c);                    }                    break;                case '}':                    if (stack.isEmpty()) {                        return false;                    }                    top = stack.getFirst();                    if (top == '{') {                        stack.removeFirst();                    } else if (top == '[' || top == '(') {                        return false;                    } else {                        stack.addFirst(c);                    }                    break;                default:                    return false;            }            index++;        }        return stack.isEmpty();    }}

Evaluation Result

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