add solution for construct binary tree from inorder and postorder

traversal

Author: freefcw

go/construct-binary-tree-from-inorder-and-postorder-traversal.go

@@ -0,0 +1,30 @@
+package leetcode
+
+func findInorderIndex(inorder []int, val int) int {
+	for pos := 0; pos < len(inorder); pos++ {
+		if inorder[pos] == val {
+			return pos
+		}
+	}
+	return -1
+}
+
+func ipbuildTree(inorder []int, postorder []int) *TreeNode {
+	// fmt.Printf("-- %v %v\n", inorder, postorder)
+	length := len(postorder)
+	if length == 0 {
+		return nil
+	}
+	root := new(TreeNode)
+	root.Val = postorder[length-1]
+	if len(postorder) == 1 {
+		return root
+	}
+
+	rootInorderPos := findInorderIndex(inorder, root.Val)
+	leftNodeNumbers := rootInorderPos
+	root.Left = ipbuildTree(inorder[:rootInorderPos], postorder[:leftNodeNumbers])
+	root.Right = ipbuildTree(inorder[rootInorderPos+1:], postorder[leftNodeNumbers:len(postorder)-1])
+
+	return root
+}

go/construct-binary-tree-from-inorder-and-postorder-traversal_test.go

@@ -0,0 +1,45 @@
+package leetcode
+
+import "testing"
+
+func TestBuildTree(t *testing.T) {
+	tests := []struct {
+		inorder   []int
+		postorder []int
+		expect    []int
+	}{
+		{
+			inorder:   []int{1, 2, 3, 4, 5},
+			postorder: []int{2, 1, 5, 4, 3},
+			expect:    []int{3, 1, 4, -1, 2, -1, 5},
+		}, {
+			inorder:   []int{1, 2, 3, 4},
+			postorder: []int{4, 3, 2, 1},
+			expect:    []int{1, -1, 2, -1, -1, -1, 3, -1, -1, -1, -1, -1, -1, -1, 4},
+		}, {
+			inorder:   []int{9, 3, 15, 20, 7},
+			postorder: []int{9, 15, 7, 20, 3},
+			expect:    []int{3, 9, 20, -1, -1, 15, 7},
+		}, {
+			inorder:   []int{9},
+			postorder: []int{9},
+			expect:    []int{9},
+		}, {
+			inorder:   []int{3, 9, 1},
+			postorder: []int{3, 9, 1},
+			expect:    []int{1, 9, -1, 3},
+		}, {
+			inorder:   []int{3, 2, 1},
+			postorder: []int{3, 2, 1},
+			expect:    []int{1, 2, -1, 3},
+		},
+	}
+
+	for i, item := range tests {
+		tree := ipbuildTree(item.inorder, item.postorder)
+		actual := treeToSlice(tree, -1)
+		if !intsEqual(item.expect, actual) {
+			t.Fatalf("\n%d\nexpect %v\nactual %v", i, item.expect, actual)
+		}
+	}
+}