1325. Delete Leaves With a Given Value.cpp

// ***
//
// 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]
//
//
// Constraints:
//
// 1 <= target <= 1000
// The given binary tree will have between 1 and 3000 nodes.
// Each node's value is between [1, 1000].
//
// ***

class Solution {
public:
    TreeNode* removeLeafNodes(TreeNode* root, int target) {
        if (not root) {
            return nullptr;
        }

        root->left = removeLeafNodes(root->left, target);
        root->right = removeLeafNodes(root->right, target);

        if (root->val == target and not root->left and not root->right) {
            return nullptr;
        }

        return root;
    }
};