0.code

class Solution {
    public int findRepeatNumber(int[] nums) {
        int len = nums.length;
        for(int i=0;i<len;i++){
            while(nums[i]!=i){
                if(nums[i]==nums[nums[i]]){
                    return nums[i];
                }
                int temp = nums[i];
                nums[i] = nums[nums[i]];
                nums[temp] = temp;
            }
        }
        return -1;
    }
}

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