1370. Increasing Decreasing String

Difficulty: Easy
323 / 323 test cases passed.
Runtime: 52 ms
Memory Usage: 14 MB

Author: YuriSpiridonov

Easy/1370.IncreasingDecreasingString.py

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+"""
+    Given a string s. You should re-order the string using the following 
+    algorithm:
+        1. Pick the smallest character from s and append it to the result.
+        2. Pick the smallest character from s which is greater than the last 
+           appended character to the result and append it.
+        3. Repeat step 2 until you cannot pick more characters.
+        4. Pick the largest character from s and append it to the result.
+        5. Pick the largest character from s which is smaller than the last 
+           appended character to the result and append it.
+        6. Repeat step 5 until you cannot pick more characters.
+        7. Repeat the steps from 1 to 6 until you pick all characters from s.
+
+    In each step, If the smallest or the largest character appears more than 
+    once you can choose any occurrence and append it to the result.
+
+    Return the result string after sorting s with this algorithm.
+
+    Example:
+    Input: s = "aaaabbbbcccc"
+    Output: "abccbaabccba"
+    Explanation: After steps 1, 2 and 3 of the first iteration, 
+                 result = "abc"
+                 After steps 4, 5 and 6 of the first iteration, 
+                 result = "abccba"
+                 First iteration is done. Now s = "aabbcc" and we go back to 
+                 step 1
+                 After steps 1, 2 and 3 of the second iteration, 
+                 result = "abccbaabc"
+                 After steps 4, 5 and 6 of the second iteration, 
+                 result = "abccbaabccba"
+
+    Example:
+    Input: s = "rat"
+    Output: "art"
+    Explanation: The word "rat" becomes "art" after re-ordering it with the 
+                 mentioned algorithm.
+
+    Example:
+    Input: s = "leetcode"
+    Output: "cdelotee"
+
+    Example:
+    Input: s = "ggggggg"
+    Output: "ggggggg"
+
+    Example:
+    Input: s = "spo"
+    Output: "ops"
+
+    Constraints:
+        - 1 <= s.length <= 500
+        - s contains only lower-case English letters.
+"""
+#Difficulty: Easy
+#323 / 323 test cases passed.
+#Runtime: 52 ms
+#Memory Usage: 14 MB
+
+#Runtime: 52 ms, faster than 96.96% of Python3 online submissions for Increasing Decreasing String.
+#Memory Usage: 14 MB, less than 100.00% of Python3 online submissions for Increasing Decreasing String.
+
+class Solution:
+    def sortString(self, s: str) -> str:
+        result = ''
+        letters = [0] * 26
+        chars = set(s)
+        for char in chars:
+            letters[ord(char) - 97] = s.count(char)
+        while True:
+            for i in range(26):
+                if letters[i]:
+                    result += chr(i + 97)
+                    letters[i] -= 1
+            for l in range(25, -1, -1):
+                if letters[l]:
+                    result += chr(l + 97)
+                    letters[l] -= 1
+            if sum(letters) == 0:
+                break
+        return result