Implement linked-list-cycle-ii

https://leetcode.com/problems/linked-list-cycle-ii

time: 16ms
time-rank: 21.04%
time-complexity: O(N)

space: 10MB
space-rank: 9.36%
space-complexity: O(N)

Fixes #228

Signed-off-by: Christopher Friedt <[email protected]>

Author: cfriedt

linked-list-cycle-ii-test.cpp

@@ -0,0 +1,64 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2018 Christopher Friedt
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include <vector>
+
+#include <gtest/gtest.h>
+
+#include "util/ListNode.cpp"
+
+#include "linked-list-cycle-ii.cpp"
+
+TEST(LinkedListCycleIi, Test_3_2_0_n4__1) {
+  vector<ListNode> nodes = {
+      ListNode(3),
+      ListNode(2),
+      ListNode(0),
+      ListNode(-4),
+  };
+  nodes[0].next = &nodes[1];
+  nodes[1].next = &nodes[2];
+  nodes[2].next = &nodes[3];
+  nodes[3].next = &nodes[1];
+  EXPECT_EQ(&nodes[1], Solution().detectCycle(&nodes[0]));
+}
+
+TEST(LinkedListCycleIi, Test_1_2__0) {
+  vector<ListNode> nodes = {
+      ListNode(1),
+      ListNode(2),
+  };
+  nodes[0].next = &nodes[1];
+  nodes[1].next = &nodes[0];
+  EXPECT_EQ(&nodes[0], Solution().detectCycle(&nodes[0]));
+}
+
+TEST(LinkedListCycleIi, Test_1_n1) {
+  vector<ListNode> nodes = {
+      ListNode(1),
+  };
+  nodes[0].val = 1;
+  nodes[0].next = NULL;
+  EXPECT_EQ(NULL, Solution().detectCycle(&nodes[0]));
+}

linked-list-cycle-ii.cpp

@@ -0,0 +1,58 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2018 Christopher Friedt
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include <unordered_set>
+
+using namespace std;
+
+// https://leetcode.com/problems/linked-list-cycle-ii
+
+class Solution {
+public:
+  ListNode *detectCycle(ListNode *head) {
+    unordered_set<ListNode *> visited;
+    ListNode *it;
+    for (it = head; it != NULL; it = it->next) {
+      if (visited.end() != visited.find(it)) {
+        return it;
+      }
+      visited.insert(it);
+    }
+    return it;
+  }
+
+  /*
+    // Recursive solution (obviously better to use iterative)
+    ListNode *helper(unordered_set<ListNode *> &visited, ListNode *n) {
+      if (NULL == n) {
+        return NULL;
+      }
+      if (visited.end() != visited.find(n)) {
+        return n;
+      }
+      visited.insert(n);
+      return helper(visited, n->next);
+    }
+  */
+};