Update 0287-find-the-duplicate-number.java

Used a do while loop to make the code more concise.

java/0287-find-the-duplicate-number.java

@@ -3,24 +3,26 @@
 // Space Complexity: O(1)
 
 class Solution {
-
  public int findDuplicate(int[] nums) {
- int fast = nums[0];
- int slow = nums[0];
- boolean first = true;
- while (first || fast != slow) {
- if (first) first = false;
+ int slow = 0;
+ int fast = 0;
+
+ do {
  slow = nums[slow];
  fast = nums[nums[fast]];
- if (fast == slow) break;
  }
- int slow2 = nums[0];
- while (slow2 != slow) {
- if (first) first = false;
- slow2 = nums[slow2];
+
+ while (slow != fast);
+
+ int slow2 = 0;
+
+ do {
  slow = nums[slow];
- if (slow2 == slow) return slow;
+ slow2 = nums[slow2];
  }
- return slow;
+
+ while (slow != slow2);
+
+ return slow2;
  }
 }