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Python program to Rearrange a string so that all same characters become d distance away
Given a non-empty string str and an integer k , rearrange the string such that the same characters are at least distance k from each other.
All input strings are given in lowercase letters. If it is not possible to rearrange the string, return an empty string "".
str = “tutorialspoint”, k = 3 Answer: “tiotiotalnprsu”
The same characters are at least 3 character distance apart.
str = "aabbcc", k = 3 Answer: "abcabc" The same characters are at least 3 character distance apart.
str = "aaabc", k = 3 Answer: "" It is not possible to rearrange the string.
str = "aaadbbcc", k = 2 Answer: "abacabcd" Another possible answer is: "abcabcda" The same characters are at least 2 character distance apart.
MAX = 128 # A structure to store a character 'char' and its frequency 'freq' # in input string class charFreq(object): def __init__(self,char,freq): self.c = char self.f = freq # A utility function to swap two charFreq items. def swap(x, y): return y, x # A utility function def toList(string): t =  for x in string: t.append(x) return t # A utility function def toString(l): return ''.join(l) # A utility function to maxheapify the node freq[i] of a heap stored in freq def maxHeapify(freq, i, heap_size): l = i*2 + 1 r = i*2 + 2 largest = i if l < heap_size and freq[l].f > freq[i].f: largest = l if r < heap_size and freq[r].f > freq[largest].f: largest = r if largest != i: freq[i], freq[largest] = swap(freq[i], freq[largest]) maxHeapify(freq, largest, heap_size) # A utility function to convert the array freq to a max heap def buildHeap(freq, n): i = (n - 1)//2 while i >= 0: maxHeapify(freq, i, n) i-=1 # A utility function to remove the max item or root from max heap def extractMax(freq, heap_size): root = freq if heap_size > 1: freq = freq[heap_size-1] maxHeapify(freq, 0, heap_size-1) return root # The main function that rearranges input string 'str' such that # two same characters become d distance away def rearrange(string, d): # Find length of input string n = len(string) # Create an array to store all characters and their # frequencies in str freq =  for x in range(MAX): freq.append(charFreq(0,0)) m = 0 # Traverse the input string and store frequencies of all # characters in freq array. for i in range(n): x = ord(string[i]) # If this character has occurred first time, increment m if freq[x].c == 0: freq[x].c = chr(x) m+=1 freq[x].f+=1 string[i] = '\0' # Build a max heap of all characters buildHeap(freq, MAX) # Now one by one extract all distinct characters from max heap # and put them back in str with the d distance constraint for i in range(m): x = extractMax(freq, MAX-i) # Find the first available position in str p = i while string[p] != '\0': p+=1 # Fill x.c at p, p+d, p+2d, .. p+(f-1)d for k in range(x.f): # If the index goes beyond size, then string cannot # be rearranged. if p + d*k >= n: print ("It is not possible to rearrange the string.") return string[p + d*k] = x.c return toString(string) string = "tutorialspoint" print (rearrange(toList(string), 3) )
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