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].
//Time: O(n), Space: O(1) public int[] twoSum(int[] nums, int target) { if (nums == null || nums.length == 0) { return null; } Map<Integer, Integer> map = new HashMap<Integer, Integer>(); int[] result = new int[2]; for (int i = 0; i < nums.length; i++) { if (map.containsKey(target - nums[i])) { result[0] = map.get(target - nums[i]); result[1] = i; break;//注意这里不要忘记跳出 } map.put(nums[i], i);//不要忘记随时更新map } return result; }
原文：https://www.cnblogs.com/jessie2009/p/9806394.html