增加demo

leetcode/.vscode/launch.json

@@ -4,6 +4,34 @@
     // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
     "version": "0.2.0",
     "configurations": [
+        {
+            "type": "java",
+            "name": "Launch L0331",
+            "request": "launch",
+            "mainClass": "practice.L0331",
+            "projectName": "leetcode_d4710210"
+        },
+        {
+            "type": "java",
+            "name": "Launch L0449",
+            "request": "launch",
+            "mainClass": "practice.L0449",
+            "projectName": "leetcode_d4710210"
+        },
+        {
+            "type": "java",
+            "name": "Launch L0606",
+            "request": "launch",
+            "mainClass": "practice.L0606",
+            "projectName": "leetcode_d4710210"
+        },
+        {
+            "type": "java",
+            "name": "Launch L0033",
+            "request": "launch",
+            "mainClass": "offer.L0033",
+            "projectName": "leetcode_d4710210"
+        },
         {
             "type": "java",
             "name": "Launch L0393",

leetcode/src/offer/L0033.java

@@ -0,0 +1,90 @@
+package offer;
+
+/**
+ * @program: leetcode
+ * @description:
+ * @author: [email protected]
+ * @create: 2022-06-30 22:33
+ **/
+public class L0033 {
+
+    private boolean verify(int[] array, int start, int end) {
+        // System.out.println("开始验证[" + start + "]-[" + end + "]，总长[" + array.length + "]");
+
+        // 终止条件
+        if (start >= end) {
+            return true;
+        }
+
+        int leftStart = start;
+        // 注意，leftEnd的默认值必须是end-1，因为一旦不存在右子树，整段都是左子树
+        int leftEnd = end-1;
+
+        int rightStart = start;
+        int rightEnd = end - 1;
+
+        boolean find = false;
+        // 先划分左右子树
+        for (int i = start; i <= end - 1; i++) {
+            // System.out.println("i=[" + i + "], array[i]=[" + array[i] + "], array[end]=" + array[end] + "]");
+            // 第一个比end大的元素，就是右子树
+            if (array[i] > array[end]) {
+                find = true;
+                // System.out.println("i=[" + i + "]");
+                leftEnd = i - 1;
+                rightStart = i;
+                break;
+            }
+        }
+
+        // System.out.println("左[" + leftStart + "]-[" + leftEnd + "]，右[" + rightStart + "]-[" + rightEnd + "]");
+
+        // 左子树都要比根节点小
+        for (int i = leftStart; i <= leftEnd; i++) {
+            if (array[i] > array[end]) {
+                // System.out.println("------1");
+                return false;
+            }
+        }
+
+        // 确实存在右子树
+        if (find) {
+            // 右子树都要比自己大
+            for (int i = rightStart; i <= rightEnd; i++) {
+                if (array[i] < array[end]) {
+                    // System.out.println("------2");
+                    return false;
+                }
+            }
+        }
+
+        // 递归校验左子树
+        if (!verify(array, leftStart, leftEnd)) {
+            // System.out.println("------3");
+            return false;
+        }
+
+        // 递归的校验右子树
+        return find ? verify(array, rightStart, rightEnd) : true;
+    }
+
+    public boolean verifyPostorder(int[] postorder) {
+        return verify(postorder, 0, postorder.length - 1);
+    }
+
+    public static void main(String[] args) {
+        // System.out.println(new L0033().verifyPostorder(new int[]{1,6,3,2,5})); //
+        // false
+        // System.out.println("");
+
+        // System.out.println(new L0033().verifyPostorder(new int[]{1,3,2,6,5})); //
+        // false
+        // System.out.println("");
+
+        // System.out.println(new L0033().verifyPostorder(new int[] { 4, 6, 7, 5 })); // true
+        // System.out.println("");
+
+        System.out.println(new L0033().verifyPostorder(new int[] { 5, 2, -17, -11, 25, 76, 62, 98, 92, 61 })); // true
+        System.out.println("");
+    }
+}

leetcode/src/practice/L0331.java

@@ -0,0 +1,130 @@
+package practice;
+
+import java.util.ArrayList;
+import java.util.Deque;
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * @program: leetcode
+ * @description:
+ * @author: [email protected]
+ * @create: 2022-06-30 22:33
+ **/
+public class L0331 {
+
+    // 9,3,4,#,#,1,#,#,2,#,6,#,#
+    /*
+    public boolean isValidSerialization(String preorder) {
+        String[] array = preorder.split(",");
+
+        Deque<String> deque = new LinkedList<String>();
+        Deque<String> temp = new LinkedList<String>();
+
+        // 入栈
+        for (int i=0;i<array.length;i++) {
+            deque.offerLast(array[i]);
+        }
+
+        String lastLast = null;;
+        String last = null;
+
+        while (!deque.isEmpty()) {
+
+            String current = deque.pollFirst();
+            // System.out.println("1. 取出了["+current+"]");
+
+            // 凑不齐三个就不用检查
+            if (null==lastLast) {
+                // System.out.println("2. 凑不齐三个");
+                temp.offerLast(current);
+                lastLast = last;
+                last = current;
+                continue;
+            }
+
+
+            // System.out.println("3. [" + lastLast + "]-[" + last + "]-[" + current + "]");
+
+            if (!"#".equals(lastLast) && "#".equals(last) && "#".equals(current)) {
+                // System.out.println("4. [" + lastLast + "]-[" + last + "]-[" + current + "]，这是个叶子结点，处理后将temp全部塞回去");
+                // 注意：刚才是从头顶取的，要从头顶塞回去
+                deque.offerFirst(current);
+
+                // temp要丢掉两个
+                temp.pollLast();
+                temp.pollLast();
+
+                while(!temp.isEmpty()) {
+                    deque.offerFirst(temp.pollLast());
+                }
+
+                // temp空了，两个变量也要清理
+                lastLast = null;
+                last = null;
+
+            } else {
+                // System.out.println("5. 不是叶子节点");
+                temp.offerLast(current);
+                lastLast = last;
+                last = current;
+            }
+        }
+
+        return 1==temp.size() && "#".equals(temp.pollFirst());
+    }
+    */
+
+    // 1. 根节点：0入，2出
+    // 2. 其他节点：1入，2出
+    // 3. null节点：1入，0出
+
+    public boolean isValidSerialization(String preorder) {
+        // 空节点，特殊
+        if ("#".equals(preorder)) {
+            return true;
+        }
+
+        int in = 0;
+        int out = 0;
+
+        String[] array = preorder.split(",");
+
+
+        for (int i=0;i<array.length;i++) {
+
+            if (0==i) {
+                // 长度大于1的时候，根节点还要等于#，就是非法
+                if ("#".equals(array[i])) {
+                    return false;
+                }
+
+                // 1. 根节点：0入，2出
+                out = 2;
+                continue;
+            }
+
+
+            if ("#".equals(array[i])) {
+                // 3. null节点：1入，0出
+                in++;
+            } else {
+                // 2. 其他节点：1入，2出
+                in++;
+                out += 2;
+            }
+
+            // 不到最后，入度一定是小于出度的
+            if (i<(array.length-1) && in>=out) {
+                return false;
+            }
+        }
+
+        return in==out;
+    }
+
+    public static void main(String[] args) {
+        System.out.println(new L0331().isValidSerialization("9,3,4,#,#,1,#,#,2,#,6,#,#"));
+        // System.out.println(new L0331().isValidSerialization("#,#,#"));
+    }
+}