Construct Binary Tree from Preorder and Inorder Traversal

Author: mengli

ConstructBinaryTreefromPreorderAndInorderTraversal.java

@@ -0,0 +1,40 @@
+/**
+ * Given preorder and inorder traversal of a tree, construct the binary tree.
+ * 
+ * Note:
+ * 
+ * You may assume that duplicates do not exist in the tree.
+ */
+
+public class ConstructBinaryTreefromPreorderAndInorderTraversal {
+	public TreeNode buildTree(int[] preorder, int[] inorder) {
+		int length1 = preorder.length;
+		int length2 = inorder.length;
+		return buildTree(preorder, 0, length1, inorder, 0, length2);
+	}
+
+	private TreeNode buildTree(int[] preorder, int s1, int e1, int[] inorder,
+			int s2, int e2) {
+		if (s1 >= e1 || s2 >= e2) {
+			return null;
+		}
+		if (s1 + 1 == e1) {
+			return new TreeNode(preorder[s1]);
+		}
+		int mid = preorder[s1];
+		int i = s2;
+		for (; i < e2; i++) {
+			if (inorder[i] == mid) {
+				break;
+			}
+		}
+		TreeNode left = buildTree(preorder, s1 + 1, s1 + 1 + i - s2, inorder,
+				s2, i);
+		TreeNode right = buildTree(preorder, s1 + 1 + i - s2, e1, inorder,
+				i + 1, e2);
+		TreeNode root = new TreeNode(preorder[s1]);
+		root.left = left;
+		root.right = right;
+		return root;
+	}
+}