1325 Delete Leaves With a Given Value¶

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 it’s parent node becomes a leaf node and has the value target, it should also be deleted (you need to continue doing that until you can’t).

Example 1:

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:

Input: root = [1,3,3,3,2], target = 3
Output: [1,3,null,null,2]

Example 3:

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.

Example 4:

Input: root = [1,1,1], target = 1
Output: []

Example 5:

Input: root = [1,2,3], target = 1
Output: [1,2,3]

Solution: Recursion¶

Post-order traversal

Time complexity: O(n) Space complexity: O(n)

class Solution {
public:
  TreeNode* removeLeafNodes(TreeNode* root, int target) {
    if (!root) return nullptr;
    root->left = removeLeafNodes(root->left, target);
    root->right = removeLeafNodes(root->right, target);
    return root->left || root->right || root->val != target
      ? root : nullptr;
  }
};