Pattern visualizer
Binary Tree Postorder Traversal
Postorder is bottom-up: a node may only report after BOTH of its subtrees are completely done, so leaves go first and the root goes last. Watch the call stack — every frame waits for the frames above it before it appends its own value. Animated on: Return the postorder traversal of the tree [1, 2, 3, 4, 5, null, 6] — expected [4,5,2,6,3,1]..
Left, right, then self
time O(n)space O(h)step 1 / 9
4
2
5
1
3
6
Call stack
postorder(1)
line 4
Enter postorder(1). Its value is NOT appended yet: postorder means both subtrees (2 and 3) must be completely finished first, so this frame parks on the stack and recurses left.
Pseudocode
1FUNCTION postorder(node, out):2 IF node = null:3 RETURN4 postorder(node.left, out)5 postorder(node.right, out)6 APPEND node.val TO out7 RETURN out
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