# Best Time to Buy and Sell Stock I,II,III

Best Time to Buy and Sell Stock I 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...

# 279. Perfect Squares

Given a positive integer n, find the least number of perfect square numbers (for example, `1, 4, 9, 16, ...`) which sum to n. For example, given n = `12`,...

# 84. Largest Rectangle in Histogram

Given n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the histogram. Above is a histogram where width ...

# 224. Basic Calculator

Implement a basic calculator to evaluate a simple expression string. The expression string may contain open `(` and closing parentheses `)`, the plus `+` or minus s...

# 134. Gas Station

Question: There are N gas stations along a circular route, where the amount of gas at station i is `gas[i]`. You have a car with an unlimited gas tank and it costs

# 42. Trapping Rain Water

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining. For example, Given [0,1,0,2,1,0,1,3,2,...

# 28. Strstr()

KMP Algorithm, Pre-compute and create the suffix equal to prefix table Next. Then if mismatch, run back the pointer of needle string according to the prefix table on the mismatch place. (e.g. misma...