problem0001

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1. Two Sum

题目

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

解题思路

a + b = target

也可以看成是

a = target - b

在map[整数]整数的序号中，可以查询到a的序号。这样就不用嵌套两个for循环了。