# Two Pointers moving in opposite directions

## Trapping Rain Water

Given a list of non-negative integers representing elevations of columns, and assuming each column is of equal width of 1, find how much water is trapped in the columns after a rain. Left and right boundaries outside of the columns have 0 elevations.

Input: `[3, 2, 1, 2, 2, 3, 2]`

Output: 5

## Try it yourself

Loading full content...