题目内容：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].
题目分析：Array Hash table
题目要求输入的是和队列的数值相关的值，输出的适合队列的索引相关的值，那么可以将队列存储在Map当中，Map中的Key是队列中的数值，Value是队列中与数值相关的索引。注意Map的定义语句：
Map <Integer, Integer> map = new HashMap <Integer, Integer>();
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