import java.util.HashMap; public class TwoSum { /** * one pass * 要注意map.put要放在for末尾，对于case[3, 3], target=6的情况，如果放在开头会覆盖第一个3 */ public int[] twoSum2(int[] nums, int target) { HashMap map = new HashMap<>(); for (int i = 0; i < nums.length; i++) { if (map.containsKey(target - nums[i])) { return new int[] {map.get(target - nums[i]), i}; } map.put(nums[i], i); } return null; } }