feat: add solutions to lc problems: No.1596,1831

* No.1596.The Most Frequently Ordered Products for Each Customer
* No.1831.Maximum Transaction Each Day

Author: yanglbme

solution/1500-1599/1596.The Most Frequently Ordered Products for Each Customer/README.md

@@ -126,26 +126,35 @@ John (customer 5) 没有订购过商品, 所以我们并没有把 John 包含在
 
 <!-- tabs:start -->
 
-### **Python3**
+### **SQL**
 
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
-```python
-
-```
-
-### **Java**
-
-<!-- 这里可写当前语言的特殊实现逻辑 -->
-
-```java
-
-```
-
-### **...**
-
-```
-
+```sql
+# Write your MySQL query statement below
+select
+    customer_id,
+    p.product_id,
+    p.product_name
+from
+    (
+        select
+            customer_id,
+            product_id,
+            rank() over(
+                partition by customer_id
+                order by
+                    count(1) desc
+            ) rk
+        from
+            Orders
+        group by
+            customer_id,
+            product_id
+    ) o
+    join Products p on o.product_id = p.product_id
+where
+    rk = 1;
 ```
 
 <!-- tabs:end -->

solution/1500-1599/1596.The Most Frequently Ordered Products for Each Customer/README_EN.md

@@ -122,22 +122,33 @@ John (customer 5) did not order anything, so we do not include them in the resul
 
 <!-- tabs:start -->
 
-### **Python3**
-
-```python
-
-```
-
-### **Java**
-
-```java
-
-```
-
-### **...**
-
-```
-
+### **SQL**
+
+```sql
+# Write your MySQL query statement below
+select
+    customer_id,
+    p.product_id,
+    p.product_name
+from
+    (
+        select
+            customer_id,
+            product_id,
+            rank() over(
+                partition by customer_id
+                order by
+                    count(1) desc
+            ) rk
+        from
+            Orders
+        group by
+            customer_id,
+            product_id
+    ) o
+    join Products p on o.product_id = p.product_id
+where
+    rk = 1;
 ```
 
 <!-- tabs:end -->

solution/1500-1599/1596.The Most Frequently Ordered Products for Each Customer/Solution.sql

@@ -0,0 +1,24 @@
+# Write your MySQL query statement below
+select
+    customer_id,
+    p.product_id,
+    p.product_name
+from
+    (
+        select
+            customer_id,
+            product_id,
+            rank() over(
+                partition by customer_id
+                order by
+                    count(1) desc
+            ) rk
+        from
+            Orders
+        group by
+            customer_id,
+            product_id
+    ) o
+    join Products p on o.product_id = p.product_id
+where
+    rk = 1;

solution/1800-1899/1831.Maximum Transaction Each Day/README.md

@@ -71,7 +71,25 @@ Result table:
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```sql
-
+# Write your MySQL query statement below
+select
+    transaction_id
+from
+    (
+        select
+            transaction_id,
+            rank() over(
+                partition by date_format(day, '%Y-%m-%d')
+                order by
+                    amount desc
+            ) rk
+        from
+            Transactions
+        order by
+            transaction_id
+    ) t
+where
+    rk = 1
 ```
 
 <!-- tabs:end -->

solution/1800-1899/1831.Maximum Transaction Each Day/README_EN.md

@@ -67,7 +67,25 @@ We order the result table by transaction_id after collecting these IDs.
 ### **SQL**
 
 ```sql
-
+# Write your MySQL query statement below
+select
+    transaction_id
+from
+    (
+        select
+            transaction_id,
+            rank() over(
+                partition by date_format(day, '%Y-%m-%d')
+                order by
+                    amount desc
+            ) rk
+        from
+            Transactions
+        order by
+            transaction_id
+    ) t
+where
+    rk = 1
 ```
 
 <!-- tabs:end -->

solution/1800-1899/1831.Maximum Transaction Each Day/Solution.sql

@@ -0,0 +1,19 @@
+# Write your MySQL query statement below
+select
+    transaction_id
+from
+    (
+        select
+            transaction_id,
+            rank() over(
+                partition by date_format(day, '%Y-%m-%d')
+                order by
+                    amount desc
+            ) rk
+        from
+            Transactions
+        order by
+            transaction_id
+    ) t
+where
+    rk = 1

solution/2400-2499/2460.Apply Operations to an Array/README.md

@@ -111,15 +111,10 @@ class Solution {
             }
         }
         int[] ans = new int[n];
-        int j = 0;
-        for (int i = 0; i < n; ++i) {
-            if (nums[i] != 0) {
-                ans[j++] = nums[i];
-            }
-        }
-        for (int i = 0; i < n; ++i) {
-            if (nums[i] == 0) {
-                ans[j++] = nums[i];
+        int i = 0;
+        for (int x : nums) {
+            if (x > 0) {
+                ans[i++] = x;
             }
         }
         return ans;