Commit 9c1520f

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O(n) time and O(n) space using BFS deque.

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Lines changed: 8 additions & 7 deletions

Original file line number	Diff line number	Diff line change
`@@ -34,18 +34,19 @@`
`34`	`34`	`# self.left = left`
`35`	`35`	`# self.right = right`
`36`	`36`	`class Solution:`
`37`		`- def findBottomLeftValue(self, root: TreeNode) -> int:`
	`37`	`+ def findBottomLeftValue(self, root: Optional[TreeNode]) -> int:`
	`38`	`+ if not root: return None`
`38`	`39`	`q = collections.deque()`
`39`	`40`	`q.append(root)`
`40`		`- bottom_left = root.val`
	`41`	`+ result = None`
`41`	`42`	`while q:`
`42`		`- length = len(q)`
`43`		`- for i in range(length):`
	`43`	`+ n = len(q)`
	`44`	`+ for x in range(n):`
`44`	`45`	`node = q.popleft()`
`45`		`- if i == 0:`
`46`		`- bottom_left = node.val`
	`46`	`+ if x == 0:`
	`47`	`+ result = node.val`
`47`	`48`	`if node.left:`
`48`	`49`	`q.append(node.left)`
`49`	`50`	`if node.right:`
`50`	`51`	`q.append(node.right)`
`51`		`- return bottom_left`
	`52`	`+ return result`

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