LeetCode 1. Two Sum

题目原文

1. Two Sum

Difficulty: Easy

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].

解法

Language: Java

方法1 92%

使用HashMap记录位置 $O(n)$

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

还可以使用排序后两根指针的方法 $O(nlogn)$