InterviewCodes/CousinsInBinaryTreeII.java at main · Tiwarishashwat/InterviewCodes · GitHub

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class Solution {
    public TreeNode replaceValueInTree(TreeNode root) {
        //bfs
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        int prevSum = root.val;
        while(!queue.isEmpty()){
            int size = queue.size();
            int curSum=0;
            for(int i=0;i<size;i++){
                TreeNode node = queue.poll();
                node.val = prevSum-node.val;
                int sibsum=0;
                if(node.left!=null){
                    sibsum+=node.left.val;
                }
                if(node.right!=null){
                    sibsum+=node.right.val;
                }
                if(node.left!=null){
                    curSum += node.left.val;
                    node.left.val = sibsum;
                    queue.offer(node.left);
                }
                if(node.right!=null){
                    curSum += node.right.val;
                    node.right.val = sibsum;
                    queue.offer(node.right);
                }
            }
            prevSum = curSum;
        }
        return root;
    }
}