diff --git a/src/leetcode/lc315_countSmaller.java b/src/leetcode/lc315_countSmaller.java
new file mode 100644
index 0000000..31f32b0
--- /dev/null
+++ b/src/leetcode/lc315_countSmaller.java
@@ -0,0 +1,97 @@
+package leetcode;
+//给定一个整数数组 nums，按要求返回一个新数组 counts。数组 counts 有该性质： counts[i] 的值是 nums[i] 右侧小于 num
+//s[i] 的元素的数量。
+//
+//
+//
+// 示例：
+//
+// 输入：nums = [5,2,6,1]
+//输出：[2,1,1,0]
+//解释：
+//5 的右侧有 2 个更小的元素 (2 和 1)
+//2 的右侧仅有 1 个更小的元素 (1)
+//6 的右侧有 1 个更小的元素 (1)
+//1 的右侧有 0 个更小的元素
+//
+//
+//
+//
+// 提示：
+//
+//
+// 0 <= nums.length <= 10^5
+// -10^4 <= nums[i] <= 10^4
+//
+// Related Topics 排序 树状数组 线段树 二分查找 分治算法
+// 👍 499 👎 0
+
+
+import javax.print.attribute.standard.NumberUp;
+import java.util.ArrayList;
+import java.util.List;
+
+//leetcode submit region begin(Prohibit modification and deletion)
+/**
+ * @author Leo
+ * @ClassName lc315_countSmaller
+ * @DATE 2020/12/4 6:11 下午
+ * @Description
+ */
+class Solution {
+    public static  List<Integer> countSmaller(int[] nums) {
+        if (nums.length < 1 || nums == null) {
+            return null;
+        }
+        int[] res = new int[nums.length];
+        process(nums, 0, nums.length - 1,res);
+        List<Integer> list = new ArrayList<Integer>(res.length);
+        for (int i = 0; i < res.length; i++) {
+            list.add(res[i]);
+        }
+        return list;
+    }
+
+    public static void process(int[] arr, int l, int r, int[] res) {
+        if (l >= r) {
+            return;
+        }
+        int m = l + ((r - l) >> 1);
+        process(arr, l, m,res);
+        process(arr, m + 1, r,res);
+        merge(arr, l, m, r, res);
+    }
+
+    private static void merge(int[] arr, int l, int m, int r, int[] res) {
+        int[] help = new int[r - l + 1];
+        int p1 = m;
+        int p2 = r;
+        int i = help.length - 1;
+        while (p1 >= l && p2 > m) {
+            res[i] += arr[p1] > arr[p2] ? (p2 - m) : 0;
+            help[i--] = arr[p1] > arr[p2] ? arr[p1--] : arr[p2--];
+        }
+        while (p1 >= l) {
+            help[i--] = arr[p1--];
+        }
+        while (p2 > m) {
+            help[i--] = arr[p2--];
+        }
+        for (i = 0; i < help.length; i++) {
+            arr[l + i] = help[i];
+        }
+    }
+}
+
+class Main_315{
+
+
+
+    public static void main(String[] args){
+        int[] nums = new int[]{3,7,5,2,6,1};
+        List<Integer> list = Solution.countSmaller(nums);
+        System.out.println(list);
+
+    }
+
+}
diff --git a/src/leo/class03_04/BiggerThanRightTwice.java b/src/leo/class03_04/BiggerThanRightTwice.java
index 44f0f92..cb36c26 100644
--- a/src/leo/class03_04/BiggerThanRightTwice.java
+++ b/src/leo/class03_04/BiggerThanRightTwice.java
@@ -199,6 +199,102 @@ class BiggerThanRightTwice3 {
     }
 }
 
+class BiggerThanRightTwice4 {
+
+    public static int biggerTwice(int[] arr) {
+        if (arr.length < 2 || arr == null) {
+            return 0;
+        }
+        return process(arr, 0, arr.length - 1);
+    }
+
+    public static int process(int[] arr, int l, int r) {
+        if (l == r) {
+            return 0;
+        }
+        int m = l + ((r - l) >> 1);
+        return process(arr, l, m) + process(arr, m + 1, r) + merge(arr, l, m, r);
+    }
+
+    private static int merge(int[] arr, int l, int m, int r) {
+        int res = 0;
+        int windowR = m + 1;
+        int i;
+        for (i = l; i <= m; i++) {
+            while (windowR <= r && arr[i] > (arr[windowR] << 1)) {
+                windowR++;
+            }
+            res += windowR - m - 1;
+        }
+        int p1= l;
+        int p2 = m + 1;
+        int[] help = new int[r - l + 1];
+        i = 0;
+        while (p1 <= m && p2 <= r) {
+            help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
+        }
+        while (p1 <= m) {
+            help[i++] = arr[p1++];
+        }
+        while (p2 <= r) {
+            help[i++] = arr[p2++];
+        }
+        for (i = 0; i < help.length; i++) {
+            arr[l + i] = help[i];
+        }
+        return res;
+
+
+    }
+
+}
+
+class BiggerThanRightTwice5 {
+    public static int biggerTwice(int[] arr) {
+        if (arr.length < 2 || arr == null) {
+            return 0;
+        }
+        return process(arr, 0, arr.length - 1);
+    }
+
+    public static int process(int[] arr, int l, int r) {
+        if (l == r) {
+            return 0;
+        }
+        int m = l + ((r - l) >> 1);
+        return process(arr, l, m) + process(arr, m + 1, r) + merge(arr, l, m, r);
+    }
+
+    private static int merge(int[] arr, int l, int m, int r) {
+        int windowR = m+1;
+        int res = 0;
+        int i = l;
+        for (; i <= m; i++) {
+            while (windowR <= r && arr[i] > (arr[windowR] << 1)) {
+                windowR++;
+            }
+            res += windowR - m - 1;
+        }
+        int p1 = l;
+        int p2 = m + 1;
+        int[] help = new int[r - l + 1];
+        i = 0;
+        while (p1 <= m && p2 <= r) {
+            help[i++] = arr[p1] <= arr[p2] ? arr[p1++] : arr[p2++];
+        }
+        while (p1 <= m) {
+            help[i++] = arr[p1++];
+        }
+        while(p2<=r){
+            help[i++] = arr[p2++];
+        }
+        for (i = 0; i < help.length; i++) {
+            arr[l + i] = help[i];
+        }
+
+        return res;
+    }
+}
 
 class TestBiggerThanRightTwice {
     public static int biggerTwice(int[] arr) {
@@ -224,7 +320,7 @@ class Main{
         for (int i = 0; i < testTime; i++) {
             int[] arr = generateRandomArray(sizeMax, range);
             int[] copyArray = copyArray(arr);
-            int res = BiggerThanRightTwice3.biggerTwice(arr);
+            int res = BiggerThanRightTwice5.biggerTwice(arr);
             int res1 = TestBiggerThanRightTwice.biggerTwice(copyArray);
             if (res != res1) {
                 System.out.println("res : " + res + " " + " res1: " + res1);
diff --git a/src/leo/class07/NodeAncestorIntersection.java b/src/leo/class07/NodeAncestorIntersection.java
new file mode 100644
index 0000000..a390484
--- /dev/null
+++ b/src/leo/class07/NodeAncestorIntersection.java
@@ -0,0 +1,11 @@
+package leo.class07;
+
+/**
+ * @author Leo
+ * @ClassName NodeAncestorIntersection
+ * @DATE 2020/12/6 9:58 上午
+ * @Description
+ * 求X祖先节点交集 先序x之前的节点与后序x之后的几点交集就是x的祖先节点
+ */
+public class NodeAncestorIntersection {
+}
diff --git a/src/leo/class07/TraversalBT.java b/src/leo/class07/TraversalBT.java
new file mode 100644
index 0000000..5d672af
--- /dev/null
+++ b/src/leo/class07/TraversalBT.java
@@ -0,0 +1,171 @@
+package leo.class07;
+
+
+import java.util.Stack;
+
+/**
+ * @author Leo
+ * @ClassName RecursiveTraversalBT
+ * @DATE 2020/12/4 4:41 下午
+ * @Description 递归遍历二叉树
+ * 先序:头左右
+ * 中序:左头右
+ * 后续:左右头
+ *
+ */
+public class TraversalBT {
+
+
+
+
+
+    public static void main(String[] args){
+        TreeNode head = new TreeNode(1);
+        head.left = new TreeNode(2);
+        head.right = new TreeNode(3);
+        head.left.left = new TreeNode(4);
+        head.left.right = new TreeNode(5);
+        head.right.left = new TreeNode(6);
+        head.right.right = new TreeNode(7);
+
+        Recursive.pre(head);
+        System.out.println();
+        UnRecursive.pre(head);
+        System.out.println("--------");
+        Recursive.in(head);
+        System.out.println();
+        UnRecursive.in(head);
+        System.out.println("---------");
+        Recursive.pos(head);
+        System.out.println();
+
+        UnRecursive.pos(head);
+        System.out.println("---------");
+
+    }
+
+}
+
+
+/**
+ * 递归序,
+ * 每个节点都会遍历三次
+ */
+class Recursive{
+
+    public static void pre(TreeNode node) {
+        if (node == null) {
+            return;
+        }
+        System.out.print(node.value+" ");
+        pre(node.left);
+        pre(node.right);
+    }
+
+    public static void in(TreeNode node) {
+        if (node == null) {
+            return;
+        }
+        in(node.left);
+        System.out.print(node.value+" ");
+        in(node.right);
+    }
+
+    public static void pos(TreeNode node) {
+        if (node == null) {
+            return;
+        }
+        pos(node.left);
+        pos(node.right);
+        System.out.print(node.value+" ");
+    }
+
+}
+
+
+class UnRecursive{
+
+
+    /**
+     * 前序:头左右
+     */
+    public static void pre(TreeNode head) {
+        if (head == null) {
+            return;
+        }
+        System.out.print("pre-order: ");
+        Stack<TreeNode> stack = new Stack<>();
+        stack.add(head);
+        while (!stack.isEmpty()) {
+            head = stack.pop();
+            System.out.print(head.value + " ");
+            if (head.right != null) {
+                stack.push(head.right);
+            }
+            if (head.left != null) {
+                stack.push(head.left);
+            }
+        }
+        System.out.println();
+    }
+
+    /**
+     * 中序:左头右
+     */
+    public static void in(TreeNode head) {
+        if (head == null) {
+            return;
+        }
+        System.out.print("in-order: ");
+        Stack<TreeNode> stack = new Stack<>();
+        TreeNode cur = head;
+        while (cur != null || !stack.isEmpty()) {
+            if (cur != null) {
+                stack.push(cur);
+                cur = cur.left;
+            }else {
+                cur = stack.pop();
+                System.out.print(cur.value + " ");
+                cur = cur.right;
+            }
+        }
+        System.out.println();
+
+    }
+
+
+
+    /**
+     * 左右头
+     */
+    public static void pos(TreeNode head){
+        if (head == null) {
+            return;
+        }
+        System.out.print("pos-order: ");
+        Stack<TreeNode> s1 = new Stack<>();
+        Stack<TreeNode> s2 = new Stack<>();
+        TreeNode cur = head;
+        s1.push(cur);
+        while (!s1.isEmpty()) {
+            cur = s1.pop();
+            s2.push(cur);
+            if (cur.left != null) {
+                s1.push(cur.left);
+            }
+            if (cur.right != null) {
+                s1.push(cur.right);
+            }
+        }
+        while (!s2.isEmpty()) {
+            System.out.print(s2.pop().value + " ");
+        }
+        System.out.println();
+
+    }
+
+}
+
+
+
+
diff --git a/src/leo/class07/TreeNode.java b/src/leo/class07/TreeNode.java
new file mode 100644
index 0000000..b8417e2
--- /dev/null
+++ b/src/leo/class07/TreeNode.java
@@ -0,0 +1,17 @@
+package leo.class07;
+
+/**
+ * @author Leo
+ * @ClassName TreeNode
+ * @DATE 2020/12/5 9:58 下午
+ * @Description
+ */
+public class TreeNode {
+    int value;
+    TreeNode left;
+    TreeNode right;
+
+    public TreeNode(int value) {
+        this.value = value;
+    }
+}