Problem (English original):
Given the root of a binary tree containing integers, return a list of all the integers in the tree ordered by column from left to right. Within each column, values should be ordered from top to bottom.
Assume a node definition (or language equivalent):
struct Node {
Node *left;
Node *right;
int val;
};
Input (example, ASCII tree):
6
/ \
3 4
/ \ / \
5 1 7 0
\ /
2 8
/ \
9 7
Output (example):
[5, 9, 3, 2, 6, 1, 7, 4, 8, 0]Summary (approach):
BFS/DFS tagging each node with (col,row) (root at col=0). Group values by col, then sort columns left→right and, within each column, sort by row top→bottom. Concatenate results. Time O(n log n), space O(n).
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