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Given a m*n grid with each cell consisting of positive, negative, or zero point. We can move across a cell only if we have positive points. Whenever we pass through a cell, points in that cell are added to our overall points, the task is to find minimum initial points to reach cell (m-1, n-1) from (0, 0) by following these certain set of rules.

There are n people in a line queuing to buy tickets, where the 0th person is at the front of the line and the (n - 1)th person is at the back of the line. You are given a 0-indexed integer array tickets of length n where the number of tickets that the ith person would like to buy is tickets[i]. Each person takes exactly 1 second to buy a ticket. A person can only buy 1 ticket at a time and has to go back to the end of the line (which happens instantaneously) in order to buy more tickets. If a person does not have any tickets left to buy, the person will leave the line. Return the time taken for the person at position k (0-indexed) to finish buying tickets.

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.