[1] Two Sum

题目

Two Sum

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.
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Example:

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

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

一：暴力搜索

两个for循环即可
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二：使用 HashMap

思路

for循环数组，从HashMap中查找结果，找到则返回结果，否则将该位放入HashMap
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代码

class Solution {
	public int[] twoSum(int[] nums, int target) {
		HashMap, Integer> map = new HashMap<>();
		int[] result = new int[2];
		map.put(nums[0], 0);
		for (int i = 1; i < nums.length; i++) {
			boolean key = map.containsKey(target - nums[i]);
			if (key) {
				result[0] = map.get(target - nums[i]);
				result[1] = i;
				break;
			}
			map.put(nums[i], i);
		}
		return result;
  }
}
​