leetcode: 669. Trim a Binary Search Tree

leetcode/0669-trim-a-binary-search-tree/README.md

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+# 669. Trim a Binary Search Tree
+
+Given the `root` of a binary search tree and the lowest and highest boundaries as `low` and `high`, trim the tree so that all its elements lies in `[low, high]`. Trimming the tree should **not** change the relative structure of the elements that will remain in the tree (i.e., any node's descendant should remain a descendant). It can be proven that there is a **unique answer**.
+
+Return **the root of the trimmed binary search tree**. Note that the root may change depending on the given bounds.
+
+**Example:**
+```
+Input: root = [1,0,2], low = 1, high = 2
+Output: [1,null,2]
+```
+
+**Constraints:**
+- The number of nodes in the tree in the range `[1, 10^4]`.
+- `0 <= Node.val <= 10^4`
+- The value of each node in the tree is **unique**.
+- `root` is guaranteed to be a valid binary search tree.
+- `0 <= low <= high <= 10^4`

leetcode/0669-trim-a-binary-search-tree/trim_bst.go

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+package leetcode
+
+// TreeNode defines a binary tree node.
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func trimBST(root *TreeNode, low int, high int) *TreeNode {
+	if root == nil {
+		return root
+	}
+	if root.Val > high {
+		return trimBST(root.Left, low, high)
+	}
+	if root.Val < low {
+		return trimBST(root.Right, low, high)
+	}
+	root.Left = trimBST(root.Left, low, high)
+	root.Right = trimBST(root.Right, low, high)
+	return root
+}

leetcode/0669-trim-a-binary-search-tree/trim_bst_test.go

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+package leetcode
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTrimBST(t *testing.T) {
+	assert := assert.New(t)
+	for _, test := range tests {
+		assert.Equal(test.expected, trimBST(test.root, test.low, test.high))
+	}
+}
+
+var tests = []struct {
+	root      *TreeNode
+	low, high int
+	expected  *TreeNode
+}{
+	{
+		root: &TreeNode{
+			Val:   1,
+			Left:  &TreeNode{Val: 0},
+			Right: &TreeNode{Val: 2},
+		},
+		low:  1,
+		high: 2,
+		expected: &TreeNode{
+			Val:   1,
+			Right: &TreeNode{Val: 2},
+		},
+	},
+	{
+		root: &TreeNode{
+			Val: 3,
+			Left: &TreeNode{
+				Val: 0,
+				Right: &TreeNode{
+					Val:  2,
+					Left: &TreeNode{Val: 1},
+				},
+			},
+			Right: &TreeNode{Val: 4},
+		},
+		low:  1,
+		high: 3,
+		expected: &TreeNode{
+			Val: 3,
+			Left: &TreeNode{
+				Val:  2,
+				Left: &TreeNode{Val: 1},
+			},
+		},
+	},
+}