814. Binary Tree Pruning
Medium
Given the
root of a binary tree, return the same tree where every subtree (of the given tree) not containing a 1 has been removed.A subtree of a node
node is node plus every node that is a descendant of node.Example 1:
Input: root = [1,null,0,0,1]
Output: [1,null,0,null,1]
Explanation:
Only the red nodes satisfy the property "every subtree not containing a 1".
The diagram on the right represents the answer.
Example 2:
Input: root = [1,0,1,0,0,0,1]
Output: [1,null,1,null,1]
Example 3:
Input: root = [1,1,0,1,1,0,1,0]
Output: [1,1,0,1,1,null,1]
Constraints:
- The number of nodes in the tree is in the range
[1, 200]. Node.valis either0or1.
Runtime: 0 ms, faster than 100%
Memory Usage: 2.2 MB, less than 68.42%
/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func pruneTree(root *TreeNode) *TreeNode {
if root == nil { return nil }
var helper func(*TreeNode) bool
helper = func(root *TreeNode) bool {
if root == nil { return false } // nil 必定不包含 1，回傳 false
l := helper(root.Left)
r := helper(root.Right)
if !l { root.Left = nil } // 沒1，修剪左邊子節點
if !r { root.Right = nil } // 沒1，修剪右邊子節點
if root.Val == 1 { return true } // 節點 value 是 1，回傳true，不要剪掉
if !l && !r { return false } // 節點 value 不是 1，子節點也都沒1，回傳false，可剪
return true
}
if !helper(root) {
return nil
}
return root
}