solve problem Decode String

Author: P-ppc

README.md

@@ -310,6 +310,7 @@ All solutions will be accepted!
 |165|[Compare Version Numbers](https://leetcode-cn.com/problems/compare-version-numbers/description/)|[java/py/js](./algorithms/CompareVersionNumbers)|Medium|
 |8|[String To Integer Atoi](https://leetcode-cn.com/problems/string-to-integer-atoi/description/)|[java/py/js](./algorithms/StringToIntegerAtoi)|Medium|
 |299|[Bulls And Cows](https://leetcode-cn.com/problems/bulls-and-cows/description/)|[java/py/js](./algorithms/BullsAndCows)|Medium|
+|394|[Decode String](https://leetcode-cn.com/problems/decode-string/description/)|[java/py/js](./algorithms/DecodeString)|Medium|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/DecodeString/README.md

@@ -0,0 +1,2 @@
+# Decode String
+We can solve this problem by stack

algorithms/DecodeString/Solution.java

@@ -0,0 +1,31 @@
+class Solution {
+    public String decodeString(String s) {
+        LinkedList<String> stack = new LinkedList<String>();
+        StringBuilder sb = new StringBuilder();
+        
+        for (char c : s.toCharArray()) {
+            if (c == ']') {
+                StringBuilder strSb = new StringBuilder();
+                while (stack.size() > 0 && !stack.peek().equals("["))
+                    strSb.insert(0, stack.pop());
+                stack.pop();
+                
+                StringBuilder intSb = new StringBuilder();
+                while (stack.size() > 0 && stack.peek().matches("\\d+"))
+                    intSb.insert(0, stack.pop());
+                
+                String temp = strSb.toString();
+                strSb = new StringBuilder();
+                for (int i = 0; i < Integer.valueOf(intSb.toString()); i++)
+                    strSb.append(temp);
+                stack.push(strSb.toString());
+            } else {
+                stack.push(String.valueOf(c));
+            }
+        }
+        
+        while (stack.size() > 0)
+            sb.append(stack.pollLast());
+        return sb.toString();
+    }
+}

algorithms/DecodeString/solution.js

@@ -0,0 +1,25 @@
+/**
+ * @param {string} s
+ * @return {string}
+ */
+var decodeString = function(s) {
+    let stack = []
+    
+    s.split('').forEach(c => {
+        if (c == ']') {
+            let tempStr = ''
+            while (stack.length > 0 && stack[stack.length - 1] != '[')
+                tempStr = stack.pop() + tempStr
+            stack.pop()
+            
+            let tempInt = ''
+            while (stack.length > 0 && /\d+/.test(stack[stack.length - 1]))
+                tempInt = stack.pop() + tempInt
+            
+            stack.push(tempStr.repeat(parseInt(tempInt)))
+        } else
+            stack.push(c)
+    })
+    
+    return stack.join('')
+};

algorithms/DecodeString/solution.py

@@ -0,0 +1,23 @@
+class Solution(object):
+    def decodeString(self, s):
+        """
+        :type s: str
+        :rtype: str
+        """
+        stack = []
+        for c in s:
+            if c == ']':
+                temp_str = ''
+                while len(stack) > 0 and stack[-1] != '[':
+                    temp_str = stack.pop() + temp_str
+                stack.pop()
+                
+                temp_int = ''
+                while len(stack) > 0 and stack[-1].isdigit():
+                    temp_int = stack.pop() + temp_int
+                
+                stack.append(int(temp_int) * temp_str)
+            else:
+                stack.append(c)
+                
+        return ''.join(stack)