27 lines
362 B
Go
27 lines
362 B
Go
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package main
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// Time: O(n^2)
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// Space: O(n)
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func numTrees(n int) int {
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if n < 3 {
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return n
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}
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trees := map[int]int{
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0: 1,
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1: 1,
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2: 2,
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}
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for c := 3; c <= n; c++ {
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s := 0
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for p := 0; p < c/2; p++ {
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s += trees[p] * trees[c-p-1] * 2
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}
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if (c-1)%2 == 0 {
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p := (c - 1) / 2
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s += trees[p] * trees[p]
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}
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trees[c] = s
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}
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return trees[n]
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}
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