Best Time to Buy and Sell Stock

Say you have an array for which the ith element is the price of a given
stock on day i.

If you were only permitted to complete at most one transaction (ie, buy
one and sell one share of the stock), design an algorithm to find the
maximum profit.
Minimum Depth of Binary Tree

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from
the root node down to the nearest leaf node.
Best Time to Buy and Sell Stock II

Say you have an array for which the ith element is the price of a given
stock on day i.

Design an algorithm to find the maximum profit. You may complete as
many transactions as you like (ie, buy one and sell one share of the
stock multiple times). However, you may not engage in multiple
transactions at the same time (ie, you must sell the stock before you
buy again).