feat(solutions): add symmetric_tree

Author: WindomZ

Diff for: README.md

@@ -34,6 +34,7 @@ If you like it then you can put a :star:**Star** on it.
 
 | # | **Problem** & **Solution** | Difficulty | Single Repetition Duration | LeetCode Run Time |
 | ---: | :----- | :----------: | ----------: | ----------: |
+|[101][Solutions-101]|[Symmetric Tree][Solutions-101-Home]|Easy|[17.6 ns/op][Solutions-101-Code] / [5 test cases][Solutions-101-Test]|4 ms|
 |[100][Solutions-100]|[Same Tree][Solutions-100-Home]|Easy|[9.12 ns/op][Solutions-100-Code] / [6 test cases][Solutions-100-Test]|0 ms|
 |[99][Solutions-99]|[Recover Binary Search Tree][Solutions-99-Home]|Hard|[94.8 ns/op][Solutions-99-Code] / [3 test cases][Solutions-99-Test]|32 ms|
 |[98][Solutions-98]|[Validate Binary Search Tree][Solutions-98-Home]|Medium|[21.0 ns/op][Solutions-98-Code] / [8 test cases][Solutions-98-Test]|8 ms|
@@ -156,6 +157,10 @@ Welcome to report bugs, suggest ideas and discuss on [issues page](https://githu
 ## License
 [![FOSSA Status](https://app.fossa.io/api/projects/git%2Bgithub.com%2FWindomZ%2Fleetcode.go.svg?type=large)](https://app.fossa.io/projects/git%2Bgithub.com%2FWindomZ%2Fleetcode.go?ref=badge_large)
 
+[Solutions-101]:https://leetcode.com/problems/symmetric-tree/
+[Solutions-101-Home]:solutions/symmetric_tree/
+[Solutions-101-Code]:solutions/symmetric_tree/symmetrictree.go
+[Solutions-101-Test]:solutions/symmetric_tree/symmetrictree_test.go#L52
 [Solutions-100]:https://leetcode.com/problems/same-tree/
 [Solutions-100-Home]:solutions/same_tree/
 [Solutions-100-Code]:solutions/same_tree/sametree.go

Diff for: solutions/symmetric_tree/NOTE_Ch-zh.md

@@ -0,0 +1,3 @@
+# 解法要点
+1. 不验证根节点的镜像
+1. 通过递归遍历方式，验证`左右`叶节和`右左`叶节点是否相等

Diff for: solutions/symmetric_tree/README.md

@@ -0,0 +1,35 @@
+# [101. Symmetric Tree](https://leetcode.com/problems/symmetric-tree/description/)
+
+## Description
+
+Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
+
+For example, this binary tree `[1,2,2,3,4,4,3]` is symmetric:
+```
+    1
+   / \
+  2   2
+ / \ / \
+3  4 4  3
+```
+
+But the following `[1,2,2,null,3,null,3]`  is not:  
+
+```
+    1
+   / \
+  2   2
+   \   \
+   3    3
+```
+
+**Note:**  
+
+Bonus points if you could solve it both recursively and iteratively.
+
+## Solution
+- [Code](symmetrictree.go)
+- [Testing](symmetrictree_test.go)
+
+## Note
+- [中文](NOTE_Ch-zh.md)

Diff for: solutions/symmetric_tree/symmetrictree.go

@@ -0,0 +1,22 @@
+package symmetrictree
+
+// TreeNode definition for a binary tree node.
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func isSymmetric(root *TreeNode) bool {
+	return isMirror(root, root)
+}
+
+func isMirror(t1, t2 *TreeNode) bool {
+	if t1 == nil && t2 == nil {
+		return true
+	}
+	if t1 == nil || t2 == nil {
+		return false
+	}
+	return t1.Val == t2.Val && isMirror(t1.Right, t2.Left) && isMirror(t1.Left, t2.Right)
+}

Diff for: solutions/symmetric_tree/symmetrictree_test.go

@@ -0,0 +1,100 @@
+package symmetrictree
+
+import (
+	"testing"
+
+	"github.com/WindomZ/testify/assert"
+)
+
+func Test_isSymmetric(t *testing.T) {
+	assert.True(t, isSymmetric(nil))
+	assert.True(t, isSymmetric(&TreeNode{Val: 0}))
+	assert.True(t, isSymmetric(&TreeNode{
+		Val: 0,
+		Left: &TreeNode{
+			Val:   1,
+			Left:  &TreeNode{Val: 1},
+			Right: &TreeNode{Val: 3},
+		},
+		Right: &TreeNode{
+			Val:   1,
+			Left:  &TreeNode{Val: 3},
+			Right: &TreeNode{Val: 1},
+		},
+	}))
+	assert.False(t, isSymmetric(&TreeNode{
+		Val: 0,
+		Left: &TreeNode{
+			Val:   1,
+			Left:  &TreeNode{Val: 1},
+			Right: &TreeNode{Val: 3},
+		},
+		Right: &TreeNode{
+			Val:   1,
+			Right: &TreeNode{Val: 1},
+		},
+	}))
+	assert.False(t, isSymmetric(&TreeNode{
+		Val: 0,
+		Left: &TreeNode{
+			Val:   1,
+			Left:  &TreeNode{Val: 1},
+			Right: &TreeNode{Val: 3},
+		},
+		Right: &TreeNode{
+			Val:   1,
+			Left:  &TreeNode{Val: 2},
+			Right: &TreeNode{Val: 1},
+		},
+	}))
+}
+
+func Benchmark_isSymmetric(b *testing.B) {
+	b.StopTimer()
+	b.ReportAllocs()
+	b.StartTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			isSymmetric(nil)
+			isSymmetric(&TreeNode{Val: 0})
+			isSymmetric(&TreeNode{
+				Val: 0,
+				Left: &TreeNode{
+					Val:   1,
+					Left:  &TreeNode{Val: 1},
+					Right: &TreeNode{Val: 3},
+				},
+				Right: &TreeNode{
+					Val:   1,
+					Left:  &TreeNode{Val: 3},
+					Right: &TreeNode{Val: 1},
+				},
+			})
+			isSymmetric(&TreeNode{
+				Val: 0,
+				Left: &TreeNode{
+					Val:   1,
+					Left:  &TreeNode{Val: 1},
+					Right: &TreeNode{Val: 3},
+				},
+				Right: &TreeNode{
+					Val:   1,
+					Right: &TreeNode{Val: 1},
+				},
+			})
+			isSymmetric(&TreeNode{
+				Val: 0,
+				Left: &TreeNode{
+					Val:   1,
+					Left:  &TreeNode{Val: 1},
+					Right: &TreeNode{Val: 3},
+				},
+				Right: &TreeNode{
+					Val:   1,
+					Left:  &TreeNode{Val: 2},
+					Right: &TreeNode{Val: 1},
+				},
+			})
+		}
+	})
+}