1325. Delete Leaves With a Given Value

Medium
Given a binary tree root and an integer target, delete all the leaf nodes with value target.
Note that once you delete a leaf node with value target, if its parent node becomes a leaf node and has the value target, it should also be deleted (you need to continue doing that until you cannot).
Example 1:
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Input: root = [1,2,3,2,null,2,4], target = 2
Output: [1,null,3,null,4]
Explanation: Leaf nodes in green with value (target = 2) are removed (Picture in left).
After removing, new nodes become leaf nodes with value (target = 2) (Picture in center).
Example 2:
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Input: root = [1,3,3,3,2], target = 3
Output: [1,3,null,null,2]
Example 3:
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Input: root = [1,2,null,2,null,2], target = 2
Output: [1]
Explanation: Leaf nodes in green with value (target = 2) are removed at each step.
Constraints:
  • The number of nodes in the tree is in the range [1, 3000].
  • 1 <= Node.val, target <= 1000

解題

/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func removeLeafNodes(root *TreeNode, target int) *TreeNode {
if root == nil { return nil }
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root.Left = removeLeafNodes(root.Left, target)
root.Right = removeLeafNodes(root.Right, target)
​
if root.Left == nil && root.Right == nil && root.Val == target{
return nil
}
​
return root
}