Calculate trapped rainwater between building heights represented as an array (Two-pointer elevation logic).

Difficulty: Hard

Phase: 6 · Mixed Logical Challenges

XP Reward: 30 XP

Topics: Mixed Logical Challenges, Hard

Supported Languages: Python, JavaScript, C, C++, Java

Problem Description

Given array of N non-negative integers representing elevation map, compute total trapped rainwater. Input Format: Read input from standard input (stdin). Output Format: Print the result to standard output (stdout).

Constraints

-10^9 <= N <= 10^9

Examples

Example 1

Input: 6 0 1 0 2 1 3

Output: 2

Explanation: Sample execution for input 6 0 1 0 2 1 3