重建二叉树，两个栈模拟一个队列

chenweijie · chenweijie · commit 50d36d5fb7e1 · 2019-04-16T00:54:35.000+08:00
diff --git a/src/main/java/com/chen/algorithm/exercise/BinaryTree.java b/src/main/java/com/chen/algorithm/exercise/BinaryTree.java
diff --git a/src/main/java/com/chen/algorithm/exercise/exercise4/BinaryTree.java b/src/main/java/com/chen/algorithm/exercise/exercise4/BinaryTree.java
@@ -0,0 +1,74 @@
+package com.chen.algorithm.exercise.exercise4;
+
+/**
+ * 重建二叉树
+ * https://www.nowcoder.com/profile/566744/codeBookDetail?submissionId=1516321
+ *
+ * @author :  chen weijie
+ * @Date: 2019-02-23 1:02 AM
+ */
+public class BinaryTree {
+
+
+    public static class TreeNode {
+
+        int val;
+
+        TreeNode left;
+
+        TreeNode right;
+
+        TreeNode(int x) {
+            val = x;
+        }
+    }
+
+
+    public static TreeNode reConstructBTree(int[] pre, int[] in) {
+        TreeNode root = reConstructBTree(pre, 0, pre.length - 1, in, 0, in.length - 1);
+        return root;
+    }
+
+
+    private static TreeNode reConstructBTree(int[] pre, int startPre, int endPre, int[] in, int startIn, int endIn) {
+
+        if (startPre > endPre || startIn > endIn) {
+            return null;
+        }
+
+        TreeNode root = new TreeNode(pre[startPre]);
+        for (int i = startIn; i <= endIn; i++) {
+            if (in[i] == pre[startPre]) {
+                root.left = reConstructBTree(pre, startPre + 1, startPre + i - startIn, in, startIn, i - 1);
+                root.right = reConstructBTree(pre, i - startIn + startPre + 1, endPre, in, i + 1, endIn);
+            }
+        }
+
+
+        return root;
+    }
+
+
+    /**
+     * 前序遍历
+     *
+     * @param current
+     */
+    public static void preOrder(TreeNode current) {
+        if (current != null) {
+            System.out.println(current.val + " ");
+            preOrder(current.left);
+            preOrder(current.right);
+        }
+    }
+
+
+    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};
+        TreeNode node = reConstructBTree(pre, in);
+        preOrder(node);
+    }
+
+
+}
diff --git a/src/main/java/com/chen/algorithm/exercise/exercise5/MyStack.java b/src/main/java/com/chen/algorithm/exercise/exercise5/MyStack.java
@@ -0,0 +1,46 @@
+package com.chen.algorithm.exercise.exercise5;
+
+/**
+ * @author :  chen weijie
+ * @Date: 2019-04-16 00:36
+ */
+public class MyStack {
+
+
+    int [] elementData;
+
+    int maxSize;
+
+    int top;
+
+
+    public MyStack(int maxSize){
+        elementData = new int[maxSize];
+        this.maxSize =maxSize;
+        top = -1;
+    }
+
+
+    public int pop(){
+        return elementData[top--];
+    }
+
+
+    public void push(int data) {
+        if (top < maxSize - 1) {
+            elementData[++top] = data;
+        }
+    }
+
+
+    public boolean isEmpty() {
+        return top == -1;
+    }
+
+
+
+
+
+
+
+}
diff --git a/src/main/java/com/chen/algorithm/exercise/exercise5/SimilarQueen.java b/src/main/java/com/chen/algorithm/exercise/exercise5/SimilarQueen.java
@@ -0,0 +1,36 @@
+package com.chen.algorithm.exercise.exercise5;
+
+/**
+ * @author :  chen weijie
+ * @Date: 2019-04-16 00:44
+ */
+public class SimilarQueen {
+
+
+    MyStack stack1 = new MyStack(10);
+
+    MyStack stack2 = new MyStack(10);
+
+
+    public void push(int data) {
+        stack1.push(data);
+    }
+
+
+    public int pop() {
+
+        if (stack1.isEmpty() && stack2.isEmpty()) {
+            throw new RuntimeException("element is empty!");
+        }
+
+        //只要栈2不为空就pop。如果栈2位空且栈1不为空，则从栈1中取出放入栈2，然后从栈2中取出。
+        if (stack2.isEmpty()) {
+            while (!stack1.isEmpty()) {
+                stack2.push(stack1.pop());
+            }
+        }
+        return stack2.pop();
+    }
+
+
+}
diff --git a/src/main/test/com/chen/test/ListNode.java b/src/main/test/com/chen/test/ListNode.java
@@ -0,0 +1,18 @@
+package com.chen.test;
+
+/**
+ * @author :  chen weijie
+ * @Date: 2019-04-15 23:18
+ */
+public class ListNode {
+
+
+    int val;
+
+    ListNode next = null;
+
+    public ListNode(int val) {
+        this.val = val;
+    }
+
+}
diff --git a/src/main/test/com/chen/test/Solution.java b/src/main/test/com/chen/test/Solution.java
@@ -0,0 +1,42 @@
+package com.chen.test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * @author :  chen weijie
+ * @Date: 2019-04-15 23:18
+ */
+public class Solution {
+
+
+    public List<Integer> outList(ListNode node) {
+
+        if (node == null) {
+            return new ArrayList<>();
+        }
+
+        ListNode head = node;
+        ListNode current = node.next;
+
+        while (current != null) {
+            ListNode temp = current.next;
+            current.next = head;
+            head = current;
+            current = temp;
+        }
+
+        node.next = null;
+
+        List<Integer> res = new ArrayList<>();
+        while (head != null) {
+            res.add(head.val);
+            head = head.next;
+        }
+        return res;
+    }
+
+
+
+
+}
