206 solved. (#53)

Author: zwfang

Makefile

@@ -4,6 +4,7 @@ GOBUILD=$(GOCMD) build
 GOCLEAN=$(GOCMD) clean
 GOTEST=$(GOCMD) test
 GOGET=$(GOCMD) get
+GOFMT=$(GOCMD) fmt
 
 test:
 	@echo "unit test"
@@ -12,3 +13,7 @@ test:
 clean:
 	@echo "clean test cache"
 	$(GOCLEAN) -testcache
+
+fmt:
+	@echo "fmt code"
+	$(GOFMT) ./...

README.md

@@ -66,6 +66,7 @@ continually updating 😃.
 * [86. Partition List](src/0086_partition_list/partition_list.go)   *`two pointers`*
 * [92. Reverse Linked List II](src/0092_reverse_linked_list_2/reverse_linked_list2.go)
 * [203. Remove Linked List Elements](src/0203_remove_linked_list_elements/remove_linked_list_elements.go)
+* [206. Reverse Linked List](src/0206_reverse_linked_list/reverse_linked_list.go)
 
 ### Dynamic Programming
 * [62. Unique Paths](./src/0062_unique_paths/unique_paths.go)   *`array`*

src/0206_reverse_linked_list/reverse_linked_list.go

@@ -0,0 +1,46 @@
+/*
+206. Reverse Linked List
+https://leetcode.com/problems/reverse-linked-list/
+
+Reverse a singly linked list.
+*/
+// time: 2019-01-07
+
+package rll
+
+// ListNode Definition for singly-linked list.
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+// recursive
+// time complexity: O(n)
+// space complexity: O(n)
+func reverseList(head *ListNode) *ListNode {
+	if head == nil || head.Next == nil {
+		return head
+	}
+
+	tail := reverseList(head.Next)
+	head.Next.Next = head
+	head.Next = nil
+	return tail
+}
+
+// iterative
+// time complexity: O(n)
+// space complexity: O(1)
+func reverseList1(head *ListNode) *ListNode {
+	var (
+		pre *ListNode
+		cur = head
+	)
+	for cur != nil {
+		next := cur.Next
+		cur.Next = pre
+		pre = cur
+		cur = next
+	}
+	return pre
+}

src/0206_reverse_linked_list/reverse_linked_list_test.go

@@ -0,0 +1,33 @@
+package rll
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestReverseList(t *testing.T) {
+	head := createSinglyLinkedList([]int{1, 2, 3, 4, 5})
+	expected := createSinglyLinkedList([]int{5, 4, 3, 2, 1})
+	if res := reverseList(head); !reflect.DeepEqual(res, expected) {
+		t.Errorf("expected %v, got %v", expected, res)
+	}
+}
+
+func TestReverseList1(t *testing.T) {
+	head := createSinglyLinkedList([]int{1, 2, 3, 4, 5})
+	expected := createSinglyLinkedList([]int{5, 4, 3, 2, 1})
+	if res := reverseList1(head); !reflect.DeepEqual(res, expected) {
+		t.Errorf("expected %v, got %v", expected, res)
+	}
+}
+
+func createSinglyLinkedList(nums []int) *ListNode {
+	head := &ListNode{}
+	cur := head
+
+	for _, num := range nums {
+		cur.Next = &ListNode{Val: num}
+		cur = cur.Next
+	}
+	return head.Next
+}

src/README.md

@@ -65,6 +65,7 @@
 |0198|[House Robber](./0198_house_robber/house_robber.go)|Easy|*`memory search;`* *`dynamic programming`*|
 |0200|[200. Number of Islands](0200_number_of_island/number_of_island.go)|Medium|*`dfs;`* *`bfs`*|
 |0203|[203. Remove Linked List Elements](0203_remove_linked_list_elements/remove_linked_list_elements.go)|Easy|*`linked list`*|
+|0206|[206. Reverse Linked List](0206_reverse_linked_list/reverse_linked_list.go)|Easy|*`linked list`*|
 |0209|[Minimum Size Subarray Sum](./0209_minimum_size_subarray_sum/minimum_size_subarray_sum.go)|Medium|*`sliding window`*|
 |0215|[215. Kth Largest Element in an Array](0215_kth_largest_element_in_an_array/kthleiaa.go)|Medium|*`sort`*|
 |0226|[Invert Binary Tree](./0226_invert_binary_tree/invert_binary_tree.go)|Easy|*`recursion; `* *`binary tree`*|