题目描述

Given an array of integers, return indices of the two numbers such that they add up to a specific target.
给定一个整数数组，返回两个数字的指数，使它们相加到特定目标。
You may assume that each input would have exactly one solution, and you may not use the same element twice.
您可以假设每个输入都具有完全一个解决方案，并且您可能不会使用* same *元素两次。

Example:

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

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

思路与实现

使用 Map ，O(n) 时间复杂度

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