题目

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

解题思路

层序遍历二叉树，每增加一层，最大深度+1.
树不能为空，二叉树可以为空，因此最大深度可以为0.

代码

maxDepth.go

package _104_Maximum_Depth_of_Binary_Tree

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

type TreeNode struct {
    Val   int
    Left  *TreeNode
    Right *TreeNode
}

func nextDepthNode(nodeSlice []*TreeNode) (nextNodeSlice []*TreeNode) {
    for _, node := range nodeSlice {
        if nil != node.Left {
            nextNodeSlice = append(nextNodeSlice, node.Left)
        }
        if nil != node.Right {
            nextNodeSlice = append(nextNodeSlice, node.Right)
        }
    }

    return nextNodeSlice
}

func MaxDepth(root *TreeNode) int {
    var maxDepth int
    if nil == root {
        return 0
    }

    nextNodeSlice := []*TreeNode{root}
    for ; len(nextNodeSlice) > 0; {
        maxDepth++
        nextNodeSlice = nextDepthNode(nextNodeSlice)
    }

    return maxDepth
}

测试代码

maxDepth_test.go

package _104_Maximum_Depth_of_Binary_Tree

import "testing"

func InitNode(val int, left *TreeNode, right *TreeNode) (ret *TreeNode){
    ret = new(TreeNode)
    ret.Val = val
    ret.Left = left
    ret.Right = right

    return ret
}

func TestMaxDepth(t *testing.T) {
    l3_1 := InitNode(3, nil, nil)
    l2_1 := InitNode(2, l3_1, nil)
    root := InitNode(1, l2_1, nil)

    want := 3
    ret := MaxDepth(root)

    if ret == want {
        t.Logf("pass")
    } else {
        t.Errorf("fail, want %+v, get %+v", want, ret)
    }
}