LeetCode OJ 1. 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.

Example:
Given nums = [2, 7, 11, 15], target = 9, Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1].

Java Code（时间复杂度为O(n)）:

class Solution {    public int[] twoSum(int[] nums, int target) {        Map<Integer, Integer> map = new HashMap<>();        int numsLength = nums.length;        for (int i = 0; i < numsLength; i++) {            int complement = target - nums[i];            if (map.containsKey(complement)) {                return new int[] {map.get(complement), i};            }            map.put(nums[i], i);        }        throw new IllegalArgumentException("No two sum solution");    }}