Refine 1323, add Java solution and link

Author: qiyuangong

README.md

@@ -224,6 +224,7 @@ I'm currently working on [Analytics-Zoo](https://github.com/intel-analytics/anal
 | 1108 | [Defanging an IP Address](https://leetcode.com/problems/defanging-an-ip-address/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1108_Defanging_an_IP_Address.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/1108_Defanging_an_IP_Address.java) | String manipulate (split, replace and join), O(n) and O(n) |
 | 1260 | [Shift 2D Grid](https://leetcode.com/problems/shift-2d-grid/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1260_Shift_2D_Grid.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/1260_Shift_2D_Grid.java) | Final position of each element can be computed according to k, m and n, e.g., k == mn, then don't move, O(mn) and O(mn) |
 | 1290 | [Convert Binary Number in a Linked List to Integer](https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1290_Convert_Binary_Number_in_a_Linked_List_to_Integer.py) | Take 2 to the power digit position from right (starting from 0) and multiply it with the digit |
+| 1323 | [Maximum 69 Number](https://leetcode.com/problems/maximum-69-number/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1323_Maximum_69_Number.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/1323_Maximum_69_Number.java) | 9 is greater than 6, so change first 6 to 9 from left if exist, O(n) and O(1) |
 | 1337 | [The K Weakest Rows in a Matrix](https://leetcode.com/problems/the-k-weakest-rows-in-a-matrix/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1337_The_K_Weakest_Rows_in_a_Matrix.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/1337_The_K_Weakest_Rows_in_a_Matrix.java) | Check by row, from left to right, until encount first zero, O(mn) and O(1) |
 | 1342 | [Number of Steps to Reduce a Number to Zero](https://leetcode.com/problems/number-of-steps-to-reduce-a-number-to-zero/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1342_Number_of_Steps_to_Reduce_a_Number_to_Zero.py) | If number is divisible by 2, divide the number by 2, else subtract 1 from the number, and output the number of steps, O(logn) and O(1) |
 | 1365 | [How Many Numbers Are Smaller Than the Current Number](https://leetcode.com/problems/how-many-numbers-are-smaller-than-the-current-number/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1365_How_Many_Numbers_Are_Smaller_Than_the_Current_Number.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/1365_How_Many_Numbers_Are_Smaller_Than_the_Current_Number.java) | 1. Sort and get position in sorted nums, O(nlogn) and O(n)<br>2. Fill count into 0-100, O(n) and O(1) |

java/1323_Maximum_69_Number.java

@@ -0,0 +1,19 @@
+class Solution {
+    public int maximum69Number (int num) {
+        // Replace first 6 with 9 if exists
+        return Integer.valueOf(String.valueOf(num).replaceFirst("6", "9"));
+    }
+
+    /*
+    public int maximum69Number (int num) {
+        char[] chars = Integer.toString(num).toCharArray();
+        // Replace first 6 with 9 if exists
+        for (int i = 0; i < chars.length; i++) {
+            if (chars[i] == '6') {
+                chars[i] = '9';
+                break;
+            }
+        }
+        return Integer.parseInt(new String(chars));
+    }*/
+}

python/1323_Maximum_69_Number.py

@@ -0,0 +1,4 @@
+class Solution:
+    def maximum69Number (self, num: int) -> int:
+        # Replace first 6 with 9 if exists
+        return(str(num).replace('6', '9', 1))