Uploaded prob 231

Problems/231.txt

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+PROBLEM 231:
+
+Given a string with repeated characters, rearrange the string so that no two adjacent characters are the same. 
+If this is not possible, return None.
+
+
+EXAMPLE:
+
+Input = "aaabbc"
+Output = "ababac"
+
+Input = "aaab"
+Output = None

Solutions/231.py

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+'''
+Problem:
+
+Given a string with repeated characters, rearrange the string so that no two adjacent characters are the same. 
+If this is not possible, return None.
+
+Example:
+
+Input = "aaabbc"
+Output = "ababac"
+
+Input = "aaab"
+Output = None
+'''
+
+def get_unique_adjacent(string):
+    length = len(string)
+    freq = {}
+
+    if (length == 0): return string
+
+    # getting the character frequency
+    for i in range(length):
+        if (string[i] in freq): freq[string[i]] += 1
+        else: freq[string[i]] = 1
+
+    sorted_freq = sorted(freq.items(), key=lambda x: x[1], reverse=True)
+    queue = list(sorted_freq)
+
+    # checking if a desired string can be formed
+    if (length % 2 == 0):
+        if (sorted_freq[0][1] > length // 2): return None
+    else:
+        if (sorted_freq[0][1] > (length // 2) + 1): return None
+
+    res = ""
+
+    # creating the required string
+    while (queue):
+        if (len(queue) == 1):
+            if (queue[0][1] == 2):
+                res = queue[0][0] + res + queue[0][0]
+                break
+            elif (queue[0][1] == 1):
+                if (res[-1] != queue[0][0]): res += queue[0][0]
+                else: res = queue[0][0] + res
+                break
+            else:
+                return None
+
+        res += queue[0][0] + queue[1][0]
+
+        queue[0] = queue[0][0], queue[0][1]-1 
+        queue[1] = queue[1][0], queue[1][1]-1 
+
+        if (len(queue) > 1 and queue[1][1] == 0): queue.pop(1)
+        if (len(queue) > 0 and queue[0][1] == 0): queue.pop(0)
+
+    return res
+
+
+# DRIVER CODE
+print(get_unique_adjacent("aaabbc"))
+print(get_unique_adjacent("aaabbcc"))
+print(get_unique_adjacent("aaabbac"))
+
+# cannot form a word of the desired form
+print(get_unique_adjacent("aaab"))
+print(get_unique_adjacent("aaabbaa"))