Sum of nodes at maximum depth of a Binary Tree

Recursive:

 maxDepthSum 함수 : 각 depth에 있는 node들의 합을 구하는 함수
maxDepth 함수에서 while 루프를 통해 최대 depth를 구한다.
leaf node의 합을 구하고 싶으므로 , depth-1 을 사용

#include <iostream>

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};

int maxDepthSum(TreeNode* root, int depth) {
    if (root == nullptr) {
        return 0;
    }

    if (depth == 0) {
        return root->val;
    }

    int leftSum = maxDepthSum(root->left, depth - 1);
    int rightSum = maxDepthSum(root->right, depth - 1);

    return leftSum + rightSum;
}

int maxDepth(TreeNode* root) {
    if (root == nullptr) {
        return 0;
    }

    int depth = 0;
    while (maxDepthSum(root, depth) != 0) {
        depth++;
    }

    return depth;
}

int main() {
    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->right = new TreeNode(3);
    root->left->left = new TreeNode(4);
    root->left->right = new TreeNode(5);

    int depth = maxDepth(root);
    int sum = maxDepthSum(root, depth - 1);

    std::cout << "Depth: " << depth << std::endl;
    std::cout << "Sum of nodes at maximum depth: " << sum << std::endl;

    return 0;
}

 

Iterative:

 

Queue 를 사용하는 것이 Key Point

while 루프에서 sum을 초기화 하므로 마지막 sum은 leaf 노드들의 합이 된다.

#include <iostream>
#include <queue>

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};

int maxDepthSum(TreeNode* root) {
    if (root == nullptr) {
        return 0;
    }

    int depth = 0;
    int sum = 0;
    std::queue<TreeNode*> q;
    q.push(root);

    while (!q.empty()) {
        int size = q.size();
        sum = 0;

        for (int i = 0; i < size; i++) {
            TreeNode* node = q.front();
            q.pop();
            sum += node->val;

            if (node->left) {
                q.push(node->left);
            }
            if (node->right) {
                q.push(node->right);
            }
        }

        depth++;
    }

    return sum;
}

int main() {
    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->right = new TreeNode(3);
    root->left->left = new TreeNode(4);
    root->left->right = new TreeNode(5);

    int sum = maxDepthSum(root);

    std::cout << "Sum of nodes at maximum depth: " << sum << std::endl;

    return 0;
}