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].
HashMap两个遍历：
public int[] twoSum(int[] nums, int target) { Map<Integer,Integer> map = new HashMap<Integer,Integer>(); 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 null; }
一次遍历：
public int[] twoSum(int[] nums, int target) { Map<Integer, Integer> map = new HashMap<>(); for (int i = 0; i < nums.length; i++) { int complement = target - nums[i]; if (map.containsKey(complement)) { return new int[] { map.get(complement), i }; } map.put(nums[i], i); } return null; }
原文：http://www.cnblogs.com/qiuhaojie/p/6628236.html