dev/leetcode/validparentheses

Valid Parentheses

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

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class Solution {
public boolean isValid(String s) {
char[] charArray = s.toCharArray();
Stack<Integer> stack = new Stack<>();
if (s == null || s.length() == 0) {
return true;
}

for (int i = 0; i < charArray.length; i++) {
if (trans(charArray[i]) > 0) {
stack.push(trans(charArray[i]));
} else if (trans(charArray[i]) < 0 ) {
if (!stack.isEmpty() && stack.pop() + trans(charArray[i]) == 0) {
continue;
} else {
return false;
}
} else {
return false;
}
}

if (stack.size() == 0) {
return true;
} else {
return false;
}
}

private int trans(char c) {
switch (c) {
case '(': return 1;
case ')': return -1;
case '[': return 2;
case ']': return -2;
case '{': return 3;
case '}': return -3;
default: return 0;
}
}

/**
执行用时 :2 ms, 在所有 Java 提交中击败了91.77%的用户
内存消耗 :37.2 MB, 在所有 Java 提交中击败了5.05%的用户
*/
}

Source code is easy to see.

Reference
https://leetcode-cn.com/problems/valid-parentheses