linked_list_cycle_II

Author: hitzzc

Diff for: README.md

@@ -125,6 +125,7 @@ Golang solution for leetcode. For each problem, there is a simple *_test.go to t
 #### [139. word break](https://github.com/hitzzc/go-leetcode/tree/master/word_break)
 #### [140. word break II](https://github.com/hitzzc/go-leetcode/tree/master/word_break_II)
 #### [141. Linked List Cycle](https://github.com/hitzzc/go-leetcode/tree/master/linked_list_cycle)
+#### [142. Linked List Cycle II](https://github.com/hitzzc/go-leetcode/tree/master/linked_list_cycle_II)
 
 
 

Diff for: linked_list_cycle_II/linked_list_cycle_II.cpp

@@ -0,0 +1,31 @@
+struct ListNode {
+	int val;
+	ListNode *next;
+	ListNode(int x) : val(x), next(NULL) {}
+};
+class Solution {
+public:
+	ListNode* detectCycle(ListNode *head) {
+		ListNode* fast = head;
+		ListNode* slow = head;
+		bool first_step = true;
+		while (first_step || fast!=slow){
+			first_step = false;
+			for (int i = 0; i < 2 && fast!=NULL; ++i) fast = fast->next;
+			if (fast==NULL) return NULL;
+			slow = slow->next;
+		}
+		int steps = 1;
+		while (fast->next != slow){
+			fast = fast->next;
+			++steps;
+		}
+		fast = slow = head;
+		for (int i = 0; i < steps; ++i) fast = fast->next;
+		while (fast!=slow){
+			fast = fast->next;
+			slow = slow->next;
+		}
+		return slow;
+	}
+};