Created
February 5, 2020 09:48
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// https://leetcode.com/problems/unique-binary-search-trees-ii | |
/** | |
* Definition for a binary tree node. | |
* type TreeNode struct { | |
* Val int | |
* Left *TreeNode | |
* Right *TreeNode | |
* } | |
*/ | |
func generateTrees(n int) []*TreeNode { | |
if n == 0 { | |
return []*TreeNode{} | |
} | |
trees := make([][][]*TreeNode, n + 2) | |
for i, _ := range trees { | |
trees[i] = make([][]*TreeNode, n + 2) | |
} | |
return generateTreesInRange(1, n, trees) | |
} | |
func generateTreesInRange(min, max int, memorized [][][]*TreeNode) []*TreeNode { | |
var trees []*TreeNode | |
for i := min; i <= max; i++ { | |
if memorized[min][i - 1] == nil { | |
memorized[min][i - 1] = generateTreesInRange(min, i - 1, memorized) | |
} | |
if memorized[i + 1][max] == nil { | |
memorized[i + 1][max] = generateTreesInRange(i + 1, max, memorized) | |
} | |
leftSubTrees := memorized[min][i - 1] | |
rightSubTrees := memorized[i + 1][max] | |
for _, left := range leftSubTrees { | |
for _, right := range rightSubTrees { | |
trees = append(trees, &TreeNode{ | |
Val: i, | |
Left: left, | |
Right: right, | |
}) | |
} | |
} | |
} | |
if len(trees) == 0 { | |
trees = append(trees, nil) | |
} | |
return trees | |
} |
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