Trapping Rain Water

Question Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining. This question is provided by LeetCode.

Valid Parentheses

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. This question is provided by Leetocode.