算法：LeetCode448_找出所有数组中消失的数字_java实现

package com.leetcode;

import java.util.*;

/**
 * LeetCode448FindDisappearedNumInArr：找出所有数组中消失的数字
 */
public class LeetCode448FindDisappearedNumInArr {

    /**
     * 方法1.hashset,找出没出现的数字
     */
    public static List<Integer> findDisappearedNumbers(int[] nums) {
        List<Integer> result = new ArrayList<>();
        if (nums == null || nums.length == 0) {
            return result;
        }
        Set<Integer> set = new HashSet<>();
        for (int num : nums) {
            set.add(num);
        }

        int n = nums.length;
        for (int i = 1; i <= n; i++) {
            if (!set.contains(i)) {
                result.add(i);
            }
        }
        return result;
    }

    /**
     *
     * @param nums
     * @return
     */
    public static List<Integer> findDisappearedNumbers2(int[] nums) {
        int n=nums.length;
        //1.对数组中数字进行遍历
        for (int num : nums) {
            //对n取模来还原出本来的值
            int x=(num-1)%n;
            nums[x]+=n;
        }

        List<Integer> result=new ArrayList<>();
        for(int i=0;i<n;i++){
            //2.找出数组中缺失的数值
            if(nums[i]<=n){
                result.add(i+1);
            }
        }
        return result;
    }

    public static void main(String[] args) {
//        int[] nums = {4, 3, 2, 7, 8, 2, 3, 1};
//        System.out.println("findDisappearedNumbers(nums) = " + findDisappearedNumbers(nums));
//        int[] nums = {1,1};
//        System.out.println("findDisappearedNumbers(nums) = " + findDisappearedNumbers(nums));

//        int[] nums = {4, 3, 2, 7, 8, 2, 3, 1};
//        System.out.println("findDisappearedNumbers2(nums) = " + findDisappearedNumbers2(nums));
        int[] nums = {1,1};
        System.out.println("findDisappearedNumbers2(nums) = " + findDisappearedNumbers2(nums));

    }
}