# 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,...

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