added diameter of binary tree solution

diameter-of-binary-tree/solution.go

@@ -0,0 +1,49 @@
+package solution
+
+// Diameter of Binary Tree
+// https://leetcode.com/explore/challenge/card/30-day-leetcoding-challenge/529/week-2/3293/
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func diameterOfBinaryTree(root *TreeNode) int {
+	if root == nil {
+		return 0
+	}
+	_, max := maxDistance(root)
+	return max
+}
+
+func maxDistance(node *TreeNode) (int, int) {
+	max, ldistance, rdistance := 0, 0, 0
+	if node.Left != nil {
+		ld, dmax := maxDistance(node.Left)
+		ldistance, max = ld+1, dmax
+
+	}
+	if node.Right != nil {
+		rd, dmax := maxDistance(node.Right)
+		rdistance = rd + 1
+		if dmax > max {
+			max = dmax
+		}
+	}
+	if d := ldistance + rdistance; d > max {
+		max = d
+	}
+	if ldistance > rdistance {
+		return ldistance, max
+	}
+	return rdistance, max
+}

diameter-of-binary-tree/solution_test.go

@@ -0,0 +1,133 @@
+package solution
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+const null = -9999999
+
+func Test_diameterOfBinaryTree(t *testing.T) {
+	tests := []struct {
+		args []int
+		want int
+	}{
+		{
+			args: []int{1},
+			want: 0,
+		},
+		{
+			args: []int{1, 2},
+			want: 1,
+		},
+		{
+			args: []int{1, 2, 3},
+			want: 2,
+		},
+		{
+			args: []int{1, 2, 3, 4, 5},
+			want: 3,
+		},
+		{
+			args: []int{1, 2, 3, 4, 5, 6},
+			want: 4,
+		},
+		{
+			args: []int{1, 2, 3, 4, 5, 6, 7},
+			want: 4,
+		},
+		{
+			args: []int{1, 2, 3, 4, 5, 6, 7, 8},
+			want: 5,
+		},
+		{
+			args: []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
+			want: 5,
+		},
+		{
+			args: []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},
+			want: 5,
+		},
+		{
+			args: []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12},
+			want: 6,
+		},
+		{
+			args: []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23},
+			want: 7,
+		},
+		{
+			args: []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25},
+			want: 8,
+		},
+		{
+			args: []int{3, 1, null, null, 2},
+			want: 2,
+		},
+		{
+			args: []int{4, 2, null, 3, 1, null, null, 5},
+			want: 3,
+		},
+		{
+			args: []int{4, -7, -3, null, null, -9, -3, 9, -7, -4, null, 6, null, -6, -6, null, null, 0, 6, 5, null, 9, null, null, -1, -4, null, null, null, -2},
+			want: 8,
+		},
+	}
+	for i, tt := range tests {
+		title := fmt.Sprintf("testcase: %d", i+1)
+		t.Run(title, func(t *testing.T) {
+			tree := genBinaryTree(tt.args)
+			if got := diameterOfBinaryTree(tree); got != tt.want {
+				t.Errorf("diameterOfBinaryTree() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestPrint(t *testing.T) {
+	v := []int{4, 2, null, 3, 1, null, null, 5}
+	tree := genBinaryTree(v)
+	printTree(t, "M", tree, 0)
+}
+
+func genBinaryTree(v []int) *TreeNode {
+	nodes := make([]*TreeNode, len(v))
+	for i := range nodes {
+		if v[i] == null {
+			continue
+		}
+		nodes[i] = &TreeNode{
+			Val: v[i],
+		}
+	}
+	cursor := 0
+	for i := 0; i < len(nodes); i++ {
+		vv := v[i]
+		if vv == null {
+			continue
+		}
+
+		left := 2*cursor + 1
+		if len(v) > left {
+			nodes[i].Left = nodes[left]
+		}
+
+		right := 2*cursor + 2
+		if len(v) > right {
+			nodes[i].Right = nodes[right]
+		}
+		cursor++
+	}
+	return nodes[0]
+}
+
+func printTree(t *testing.T, s string, tree *TreeNode, indent int) {
+	t.Logf("[%s] %s: %d", s, strings.Repeat("-", indent), tree.Val)
+	if tree.Left != nil {
+		printTree(t, "L", tree.Left, indent+2)
+	}
+	if tree.Right != nil {
+		printTree(t, "R", tree.Right, indent+2)
+	}
+}