feat: solved 287

Author: fghpdf

src/com/fghpdf/FindTheDuplicateNumber/Solution.java

@@ -0,0 +1,31 @@
+package com.fghpdf.FindTheDuplicateNumber;
+
+/**
+ * @author fghpdf
+ * @date 2019/12/23
+ * https://leetcode.com/problems/find-the-duplicate-number/
+ * fast and slow
+ * When fast==slow, they meet at the entry point of the circle
+ **/
+public class Solution {
+	public int findDuplicate3(int[] nums) {
+		if (nums.length < 1) {
+			return -1;
+		}
+
+		int slow = nums[0];
+		int fast = nums[slow];
+		while (slow != fast) {
+			slow = nums[slow];
+			fast = nums[nums[fast]];
+		}
+
+		fast = 0;
+		while (slow != fast) {
+			fast = nums[fast];
+			slow = nums[slow];
+		}
+
+		return slow;
+	}
+}