add Solution for problem 95 [golang]

Author: lightfish-zhang

solution/0095.Unique Binary Search Trees II/Solution.go

@@ -0,0 +1,68 @@
+/**
+ * @lc app=leetcode.cn id=95 lang=golang
+ * Accepted
+ * 9/9 cases passed (28 ms)
+ * Your runtime beats 94 % of golang submissions
+ * Your memory usage beats 100 % of golang submissions (8 MB)
+ */
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+
+type Pair struct {
+	a, b interface{}
+}
+
+func generateTrees(n int) []*TreeNode {
+	if n < 1 {
+		return []*TreeNode{}
+	}
+	cache := make(map[Pair][]*TreeNode)
+	return createTrees(1, n, cache)
+}
+
+func createTrees(start, end int, cache map[Pair][]*TreeNode) []*TreeNode {
+	var ret []*TreeNode
+	p := Pair{start, end}
+	if ret, ok := cache[p]; ok {
+		return ret
+	}
+	if start > end {
+		ret = []*TreeNode{nil}
+		cache[p] = ret
+		return ret
+	}
+	if start == end {
+		node := &TreeNode{
+			Val:   start,
+			Left:  nil,
+			Right: nil,
+		}
+		ret = []*TreeNode{node}
+		cache[p] = ret
+		return ret
+	}
+	ret = make([]*TreeNode, 0)
+	for i := start; i <= end; i++ {
+		lefts := createTrees(start, i-1, cache)
+		rights := createTrees(i+1, end, cache)
+		for _, left := range lefts {
+			for _, right := range rights {
+				node := &TreeNode{
+					Val:   i,
+					Left:  left,
+					Right: right,
+				}
+				ret = append(ret, node)
+			}
+		}
+	}
+	cache[p] = ret
+	return ret
+}