剑指 Offer 03. 数组中重复的数字

输入：
[2, 3, 1, 0, 2, 5, 3]
输出：2 或 3 

  class Solution1 {
        public int findRepeatNumber(int[] nums) {
            Set<Integer> set = new HashSet<Integer>();
            int repeat = -1;
            for (int num : nums) {
                if (!set.add(num)) {
                    repeat = num;
                    break;
                }
            }
            return repeat;
        }
    }

class Solution2 {
        public int findRepeatNumber(int[] nums) {
            int temp;
            for (int i = 0; i < nums.length; i++) {
                while (nums[i] != i) {
                    if (nums[i] == nums[nums[i]]) {
                        return nums[i];
                    }
                    temp = nums[i];
                    nums[i] = nums[temp];
                    nums[temp] = temp;
                }
            }
            return -1;
        }
    }