# 2641. Cousins in Binary Tree II
###### tags: `Leetcode` `Medium` `BFS` `Tree`
Link: https://leetcode.com/problems/cousins-in-binary-tree-ii/description/
## 思路
层序遍历
先算出当前一行所有children node的val sum
然后对当前一行的node的所有children node赋值
当前node的children的新val就是sum-当前node的children的val和
## Code

class Solution {
    public TreeNode replaceValueInTree(TreeNode root) {
        Queue<TreeNode> q = new LinkedList<>();
        root.val = 0;
        q.add(root);
        while(!q.isEmpty()){
            int size = q.size();
            int sum = 0;
            List<TreeNode> temp = new ArrayList<>();
            for(int i=0; i<size; i++){
                TreeNode curr = q.poll();
                temp.add(curr);
                if(curr.left!=null){
                    sum += curr.left.val;
                    q.add(curr.left);
                }
                if(curr.right!=null){
                    sum += curr.right.val;
                    q.add(curr.right);
                }
            }
            for(TreeNode curr:temp){
                int t = sum;
                if(curr.left!=null) t -= curr.left.val;
                if(curr.right!=null) t -= curr.right.val;
                if(curr.left!=null) curr.left.val = t;
                if(curr.right!=null) curr.right.val = t;
            }
        }
        return root;
    }
}