题目

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants. The tree s could also be considered as a subtree of itself.

Example 1:
Given tree s:

     3
    / \
   4   5
  / \
 1   2

Given tree t:

   4 
  / \
 1   2

Return true, because t has the same structure and node values with a subtree of s.
Example 2:
Given tree s:

     3
    / \
   4   5
  / \
 1   2
    /
   0

Given tree t:

   4
  / \
 1   2

Return false.

解题思路

如果t是s的子树，则s必有一个子树和t相等。因此遍历s，所有s的子树和t相比，如果有相等的就说明t是s的子树
注意
找到子树后就不再进行遍历

if subTree {
        return 
}

代码

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isTreeEqual(s *TreeNode, t *TreeNode) bool {
    if nil == s && nil == t {
        return true
    } else if nil != s && nil == t {
        return false
    } else if nil == s && nil != t {
        return false
    }

    if s.Val != t.Val {
        return false
    }
    if !isTreeEqual(s.Left, t.Left) {
        return false
    }
    if !isTreeEqual(s.Right, t.Right) {
        return false
    }

    return true
}

var subTree bool

func travelTree(s *TreeNode, t *TreeNode)  {
    //already find subtree
    if subTree {
        return 
    }
    
    if nil == s {
        return
    }

    if isTreeEqual(s, t) {
        subTree = true
        return
    }

    travelTree(s.Left, t)
    travelTree(s.Right, t)
}

func isSubtree(s *TreeNode, t *TreeNode) bool {
    subTree = false

    travelTree(s, t)
    return subTree
}