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].

大致意思是,有一个数组,和一个指定值,求数组中两个元素相加等于这个指定值的时候,给出两个元素的索引,相同元素不能用两次。

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

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