public int findDuplicate(int[] nums) {
int start = 0, end = nums.length - 1, mid = 0;
while (start + 1 < end) {
mid = start + (end - start) / 2;
int count = countNum(nums, mid);
return countNum(nums, start) > start ? start : end;
public int countNum(int[] nums, int target) {