寻找重复数

解题思路：二分法。在区间[1, n]中搜索，首先求出中点mid，然后遍历整个数组，统计所有小于等于mid的数的个

数，如果个数小于等于mid，则说明重复值在[mid+1, n]之间，反之，重复值应在[1, mid-1]之间，然后依次类推，

直到搜索完成，此时的right就是我们要求的重复值。 

    public int findDuplicate(int[] nums) 
    {
    	int low = 0;
    	int high = nums.length-1;
    	int mid = 0, count = 0;
    	
    	while (low < high)
    	{
    		mid = (low + high) / 2;
    		count = 0;
    		for (int num: nums)
    		{
    			if (num <= mid)
    				count++;
    		}
    		
    		if (count <= mid)
    			low = mid + 1;
    		else
    			high = mid;
    	}
    	return low;
    }