題目

Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

Example:
Given a binary tree

          1
         / \
        2   3
       / \     
      4   5    

Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

Note: The length of path between two nodes is represented by the number of edges between them.

解題思路

遍歷二叉樹，求每個節點的左子樹深度和右子樹深度和的最大值。

代碼

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
var maxDiameter int
func MaxDeepth(t *TreeNode) (deepth int)  {
    if nil == t {
        return 0
    }

    left := MaxDeepth(t.Left)
    right := MaxDeepth(t.Right)

    maxDiameter = int(math.Max(float64(maxDiameter), float64(left + right)))

    return  int(math.Max(float64(left), float64(right))) + 1
}

func diameterOfBinaryTree(root *TreeNode) int {
    maxDiameter = 0
    if nil == root {
        return 0
    }

    MaxDeepth(root)

    return maxDiameter
}