solve problem Base 7

Author: P-ppc

README.md

@@ -129,6 +129,7 @@ All solutions will be accepted!
 |455|[assign cookies](https://leetcode-cn.com/problems/assign-cookies/description/)|[java/py/js](./algorithms/AssignCookies)|Easy|
 |415|[Add Strings](https://leetcode-cn.com/problems/add-strings/description/)|[java/py/js](./algorithms/AddStrings)|Easy|
 |67|[Add Binary](https://leetcode-cn.com/problems/add-binary/description/)|[java/py/js](./algorithms/AddBinary)|Easy|
+|504|[Base 7](https://leetcode-cn.com/problems/base-7/description/)|[java/py/js](./algorithms/Base7)|Easy|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/Base7/README.md

@@ -0,0 +1,2 @@
+# Base 7
+This problem is easy to solve

algorithms/Base7/Solution.java

@@ -0,0 +1,22 @@
+    class Solution {
+    public String convertToBase7(int num) {
+        String res = "";
+        boolean isNegative = false;
+        
+        if (num == 0) {
+            res = "0";
+        } else {
+            if (num < 0) {
+                num = -num;
+                isNegative = true;
+            }
+            
+            while (num > 0) {
+                res = String.valueOf(num % 7) + res;
+                num /= 7;
+            }
+        }
+        
+        return isNegative ? "-" + res : res;
+    }
+}

algorithms/Base7/solution.js

@@ -0,0 +1,24 @@
+/**
+ * @param {number} num
+ * @return {string}
+ */
+var convertToBase7 = function(num) {
+    let res = '',
+        isNegative = false
+    
+    if (num === 0) {
+        res = '0'
+    } else {
+        if (num < 0) {
+            num = -num
+            isNegative = true
+        }
+        
+        while (num > 0) {
+            res = String(num % 7) + res
+            num = parseInt(num / 7)
+        }
+    }
+    
+    return isNegative ? '-' + res : res
+};

algorithms/Base7/solution.py

@@ -0,0 +1,18 @@
+class Solution(object):
+    def convertToBase7(self, num):
+        """
+        :type num: int
+        :rtype: str
+        """
+        res = ''
+        is_negative = False
+        
+        if num == 0:
+            res = '0'
+        if num < 0:
+            num = -num
+            is_negative = True
+        while num > 0:
+            res = str(num % 7) + res
+            num = num / 7
+        return '-' + res if is_negative else res