572. Subtree of Another Tree ⭐

Medium

Given the roots of two binary trees root and subRoot, return true if there is a subtree of root with the same structure and node values of subRoot and false otherwise.

A subtree of a binary tree tree is a tree that consists of a node in tree and all of this node's descendants. The tree tree could also be considered as a subtree of itself.

Example 1:

Input: root = [3,4,5,1,2], subRoot = [4,1,2]
Output:
 true

Example 2:

Input: root = [3,4,5,1,2,null,null,null,null,0], subRoot = [4,1,2]
Output:
 false

Constraints:

• The number of nodes in the root tree is in the range [1, 2000].

• The number of nodes in the subRoot tree is in the range [1, 1000].

• -104 <= root.val <= 104

• -104 <= subRoot.val <= 104

解題

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isSubtree(root *TreeNode, subRoot *TreeNode) bool {
    if root == nil {
        return false
    }

    if isSame(root, subRoot) { return true }

    return isSubtree(root.Left, subRoot) || isSubtree(root.Right, subRoot)
}

func isSame(root *TreeNode, subRoot *TreeNode) bool {
    if root == nil && subRoot == nil { return true }
    if root == nil || subRoot == nil { return false }
    if root.Val != subRoot.Val { return false }

    return isSame(root.Left, subRoot.Left) && isSame(root.Right, subRoot.Right)
}