To Offer | 03. Repeat Numbers in the array

The sword refers to Offer 03. Repeated numbers in an array - LeetCode(LeetCode)https://leetcode.cn/problems/shu-zu-zhong-zhong-fu-de-shu-zi-lcof/Open a pit today and brush a wave of sword offers (although I have brushed a little bit...

Method 1: Make use of the features of HashSet that can be quickly searched, put elements into HashSet and compare.

class Solution {public int findRepeatNumber(int[] nums) {HashSet integers = new HashSet<>();for (int i = 0; i < nums.length; i++) {if (integers.contains(nums[i])) {return nums[i];}integers.add(nums[i]);}return -1;}}

Method 2: Subscript method, constantly exchange elements so that the elements are the same as their corresponding subscripts until a conflict occurs.

class Solution {public int findRepeatNumber(int[] nums) {// loop through the arrayfor(int i = 0; i < nums.length; i++) {// The reason for using while is because after the swap, the element at that position is still not in the correct positionwhile(i != nums[i]){if(nums[i] == nums[nums[i]]){return nums[i];}// nums[i] is in the correct position at nums[nums[i]]int k = nums[nums[i]];nums[nums[i]] = nums[i];nums[i] = k;}}return -1;}}