LeetCode20：validParentheses

validParentheses

題目描述

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Note that an empty string is also considered valid.

Example 1:

Input: "()" Output: true Example 2:

Input: "()[]{}" Output: true Example 3:

Input: "(]" Output: false Example 4:

Input: "([)]" Output: false Example 5:

Input: "{[]}" Output: true

思路

• 使用棧方法，遍歷字符串
• 若是當前字符爲左邊括號時，直接將其壓入棧
• 若是遇到右半邊括號時，分類討論：
  • 1.若是棧不爲空，驗證是否對應左邊的括號，取出棧頂元素，繼續循環、
  • 若這時棧爲空，則直接返回false
  • 若不爲對應的左邊括號，返回false

實現思路

1.使用棧方法（使用數組的push()和pop()來模擬）

代碼

var isValid = function(s) {
  let valid = true
  const stack = []
  const mapper = {
    '{': '}',
    '(': ')',
    '[': ']'
  }
  if (s === '') {
    return valid;
  }
  for (let value of s) {
    let v = value;
    if (['{', '(', '['].indexOf(v) != -1) {
      stack.push(v)
    } else {
      if (stack.length == 0) {
        valid = false;
      } else {
        const va = stack.pop()
        if (mapper[va] != v) {
          valid = false;
        }
      }
    }
  }
  return valid;
}