Create FindtheDuplicateNumber.cpp

Week 4/FindtheDuplicateNumber.cpp

@@ -0,0 +1,29 @@
+/*
+Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one.
+
+Example 1:
+
+Input: [1,3,4,2,2]
+Output: 2
+Example 2:
+
+Input: [3,1,3,4,2]
+Output: 3
+*/
+class Solution {
+public:
+int findDuplicate(vector<int>& nums) {
+  int slow=0,fast=0;
+  while(fast<nums.size()&&nums[fast]<nums.size()){
+    slow=nums[slow];
+    fast=nums[nums[fast]];
+    if(slow==fast)  break;
+  }
+  slow=0;
+  while(slow!=fast){
+    slow=nums[slow];
+    fast=nums[fast];
+  }
+  return fast;
+}
+};