Trapping Rain Water

Given an array representing elevation map where the width of each bar is 1, compute how much water it can trap after raining. The input is a list of non-negative integers, and the output is a single integer representing the total amount of trapped water. Example Input: [0,1,0,2,1,0,1,3,2,1,2,1] Output: 6 Constraints The array length is in the range [1, 100000]. Each element is in the range [0, 100000]. Example Input 0,1,0,2,1,0,1,3,2,1,2,1