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.
使用hash
public int[] twoSum(int[] nums, int target) { int[] res = new int[2]; if (nums == null || nums.length < 2) { return res; } HashMap<Integer, Integer> map = new HashMap<Integer, Integer>(); int n = nums.length; for (int i = 0; i < n; i++) { if (map.containsKey(target - nums[i])) { res[0] = map.get(target - nums[i]); res[1] = i; return res; } map.put(nums[i], i); } return res; }