添加 problem 102

Algorithms/102. Binary Tree Level Order Traversal/102. Binary Tree Level Order Traversal.go

@@ -0,0 +1,41 @@
+package leetcode
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func levelOrder(root *TreeNode) [][]int {
+	if root == nil {
+		return [][]int{}
+	}
+	queue := []*TreeNode{}
+	queue = append(queue, root)
+	curNum, nextLevelNum, res, tmp := 1, 0, [][]int{}, []int{}
+	for len(queue) != 0 {
+		if curNum > 0 {
+			node := queue[0]
+			if node.Left != nil {
+				queue = append(queue, node.Left)
+				nextLevelNum++
+			}
+			if node.Right != nil {
+				queue = append(queue, node.Right)
+				nextLevelNum++
+			}
+			curNum--
+			tmp = append(tmp, node.Val)
+			queue = queue[1:]
+		}
+		if curNum == 0 {
+			res = append(res, tmp)
+			curNum = nextLevelNum
+			nextLevelNum = 0
+			tmp = []int{}
+		}
+	}
+	return res
+}

Algorithms/102. Binary Tree Level Order Traversal/102. Binary Tree Level Order Traversal_test.go

@@ -0,0 +1,54 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question102 struct {
+	para102
+	ans102
+}
+
+// para 是参数
+// one 代表第一个参数
+type para102 struct {
+	one []int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans102 struct {
+	one [][]int
+}
+
+func Test_Problem102(t *testing.T) {
+
+	qs := []question102{
+
+		question102{
+			para102{[]int{}},
+			ans102{[][]int{}},
+		},
+
+		question102{
+			para102{[]int{1}},
+			ans102{[][]int{[]int{1}}},
+		},
+
+		question102{
+			para102{[]int{3, 9, 20, NULL, NULL, 15, 7}},
+			ans102{[][]int{[]int{3}, []int{9, 20}, []int{15, 7}}},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 102------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans102, q.para102
+		fmt.Printf("【input】:%v      ", p)
+		root := Ints2TreeNode(p.one)
+		fmt.Printf("【output】:%v      \n", levelOrder(root))
+	}
+	fmt.Printf("\n\n\n")
+}

Algorithms/102. Binary Tree Level Order Traversal/README.md

@@ -0,0 +1,35 @@
+# [102. Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/)
+
+## 题目
+
+
+Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).
+
+For example:
+Given binary tree [3,9,20,null,null,15,7],
+
+```c
+    3
+   / \
+  9  20
+    /  \
+   15   7
+```
+
+return its level order traversal as:
+
+```c
+[
+  [3],
+  [9,20],
+  [15,7]
+]
+```
+ 
+
+## 题目大意
+
+按层序从上到下遍历一颗树。用一个队列即可实现。
+
+
+