Goldman Sachs

Given an array representing the height of bars, calculate how much water can be trapped between them after rain. Think about finding the maximum height to the left and right of each bar.

Find the minimum sum of a path from the top-left to the bottom-right corner of a grid. You can only move down or right at each step.

Find the first character in a string that appears only once. If no such character exists, return a specified value.