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Java-based LeetCode algorithm problem solutions, regularly updated
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package g2601_2700.s2641_cousins_in_binary_tree_ii;

// #Medium #Hash_Table #Depth_First_Search #Breadth_First_Search #Tree #Binary_Tree
// #2023_09_05_Time_24_ms_(72.10%)_Space_90.1_MB_(20.69%)

import com_github_leetcode.TreeNode;
import java.util.ArrayList;
import java.util.List;

/*
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
/**
 * 2641 - Cousins in Binary Tree II\.
 *
 * Medium
 *
 * Given the `root` of a binary tree, replace the value of each node in the tree with the **sum of all its cousins' values**.
 *
 * Two nodes of a binary tree are **cousins** if they have the same depth with different parents.
 *
 * Return _the_ `root` _of the modified tree_.
 *
 * **Note** that the depth of a node is the number of edges in the path from the root node to it.
 *
 * **Example 1:**
 *
 * ![](https://assets.leetcode.com/uploads/2023/01/11/example11.png)
 *
 * **Input:** root = [5,4,9,1,10,null,7]
 *
 * **Output:** [0,0,0,7,7,null,11]
 *
 * **Explanation:** The diagram above shows the initial binary tree and the binary tree after changing the value of each node. 
 * - Node with value 5 does not have any cousins so its sum is 0. 
 * - Node with value 4 does not have any cousins so its sum is 0. 
 * - Node with value 9 does not have any cousins so its sum is 0. 
 * - Node with value 1 has a cousin with value 7 so its sum is 7. 
 * - Node with value 10 has a cousin with value 7 so its sum is 7. 
 * - Node with value 7 has cousins with values 1 and 10 so its sum is 11.
 *
 * **Example 2:**
 *
 * ![](https://assets.leetcode.com/uploads/2023/01/11/diagram33.png)
 *
 * **Input:** root = [3,1,2]
 *
 * **Output:** [0,0,0]
 *
 * **Explanation:** The diagram above shows the initial binary tree and the binary tree after changing the value of each node.
 * - Node with value 3 does not have any cousins so its sum is 0. 
 * - Node with value 1 does not have any cousins so its sum is 0. 
 * - Node with value 2 does not have any cousins so its sum is 0.
 *
 * **Constraints:**
 *
 * *   The number of nodes in the tree is in the range [1, 10⁵].
 * *   1 <= Node.val <= 10⁴
**/
public class Solution {
    private List horizontalSum;

    private void traverse(TreeNode root, int depth) {
        if (root == null) {
            return;
        }
        if (depth < horizontalSum.size()) {
            horizontalSum.set(depth, horizontalSum.get(depth) + root.val);
        } else {
            horizontalSum.add(root.val);
        }
        traverse(root.left, depth + 1);
        traverse(root.right, depth + 1);
    }

    private void traverse1(TreeNode root, int depth) {
        if (root == null) {
            return;
        }
        if (depth > 0) {
            int sum = 0;
            if (root.left != null) {
                sum += root.left.val;
            }
            if (root.right != null) {
                sum += root.right.val;
            }
            if (root.left != null) {
                root.left.val = horizontalSum.get(depth + 1) - sum;
            }
            if (root.right != null) {
                root.right.val = horizontalSum.get(depth + 1) - sum;
            }
        }
        traverse1(root.left, depth + 1);
        traverse1(root.right, depth + 1);
    }

    public TreeNode replaceValueInTree(TreeNode root) {
        horizontalSum = new ArrayList<>();
        root.val = 0;
        if (root.left != null) {
            root.left.val = 0;
        }
        if (root.right != null) {
            root.right.val = 0;
        }
        traverse(root, 0);
        traverse1(root, 0);
        return root;
    }
}