26 lines
819 B
Kotlin
26 lines
819 B
Kotlin
/**
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* Example:
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* var ti = TreeNode(5)
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* var v = ti.`val`
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* Definition for a binary tree node.
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* class TreeNode(var `val`: Int) {
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* var left: TreeNode? = null
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* var right: TreeNode? = null
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* }
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*/
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class Solution {
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private data class SpecialRange(val min: Int? = null, val max: Int? = null) {
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fun check(x: Int): Boolean =
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(min == null || x > min) && (max == null || x < max)
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}
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private fun isValidBST(root: TreeNode?, range: SpecialRange): Boolean =
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when (root) {
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null -> true
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else -> range.check(root.`val`)
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&& isValidBST(root.left, range.copy(max=root.`val`))
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&& isValidBST(root.right, range.copy(min=root.`val`))
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}
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fun isValidBST(root: TreeNode?): Boolean = isValidBST(root, SpecialRange())
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}
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