problem7

Problem7/ConstructTree.java

@@ -0,0 +1,46 @@
+/**
+ * Created by owen on 2017/6/30.
+ */
+public class ConstructTree {
+    public PBinaryTreeNode constructCore(int[] pre, int[] in) {
+        if (pre.length!=in.length||pre==null||in==null){
+            //无效输入 抛出异常
+        }
+        return constructCore(pre, in, 0, pre.length - 1, 0, in.length - 1);
+    }
+
+    private PBinaryTreeNode constructCore(int[] pre, int[] in, int startPre, int endPre, int startIn, int endIn) {
+        if (startPre>endPre||startIn>endIn||endPre-startPre!=endIn-startIn) {
+            //无效输入 抛出异常
+        }
+        PBinaryTreeNode root = new PBinaryTreeNode();
+        int rootVal = pre[startPre];
+        root.value = rootVal;
+        root.left = root.right = root.parent = null;
+        //递归基本条件
+        if (startPre == endPre) {
+            if (endIn == startIn && pre[startPre] == in[startIn]) {
+                return root;
+            } else {//抛出异常
+            }
+        }
+        //在中序遍历中找到rootVal
+        int rootIn = startIn;
+        while(in[rootIn]!=rootVal&&rootIn<endIn)
+            ++rootIn;
+        if (in[rootIn]!=rootVal&&rootIn==endIn) {
+            //抛出异常
+        }
+
+        //构建左子树
+        int length = rootIn-startIn;
+        if(length>0){
+            root.left= constructCore(pre,in,startPre+1,startPre+length,startIn,rootIn-1);
+        }
+        //构建右子树
+        if (length<endPre-startPre){
+            root.right = constructCore(pre,in,startPre+length+1,endPre,rootIn+1,endIn);
+        }
+        return root;
+    }
+}

Problem7/Trst7.java

@@ -0,0 +1,14 @@
+/**
+ * Created by owen on 2017/6/30.
+ */
+public class Trst7 {
+    public static void main(String[] args) {
+        int[] pre={1,2,4,7,3,5,6,8};
+        int[] in = {4,7,2,1,5,3,8,6};
+        ConstructTree constructTree = new ConstructTree();
+        PBinaryTreeNode root = constructTree.constructCore(pre,in);
+        //先序遍历验证
+        PBinaryTreeNode.preOrder(root);
+    }
+
+}

util/PBinaryTreeNode.java

@@ -0,0 +1,15 @@
+/**
+ * Created by owen on 2017/6/30.
+ */
+public final class PBinaryTreeNode {
+    PBinaryTreeNode left;
+    PBinaryTreeNode right;
+    PBinaryTreeNode parent;
+    int value;
+    public static void preOrder(PBinaryTreeNode root){
+        if(root==null)return;
+        System.out.println(root.value);
+        preOrder(root.left);
+        preOrder(root.right);
+    }
+}