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Partition around in a pivot in O(N) time and memory
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| using System; | |
| using System.Linq; | |
| class Something | |
| { | |
| public static void Main(string[] args) | |
| { | |
| var blah = Console.ReadLine().Split(' ').Select(int.Parse).ToArray(); | |
| PrintArray(blah); | |
| Partition(blah, 9); | |
| PrintArray(blah); | |
| } | |
| static void PrintArray(int[] arr) | |
| { | |
| foreach(var elem in arr) | |
| { | |
| Console.Write(elem + " "); | |
| } | |
| Console.WriteLine(); | |
| } | |
| static void Partition(int[] arr, int pivotIdx) | |
| { | |
| var pivotValue = arr[pivotIdx]; | |
| Console.WriteLine("Pivoting on {0}", pivotValue); | |
| int tmp; | |
| // swap pivot to arr[0] | |
| if(pivotIdx > 0){ | |
| tmp = arr[0]; | |
| arr[0] = pivotValue; | |
| arr[pivotIdx] = tmp; | |
| } | |
| int j = 1; | |
| for(int i = 1; i < arr.Length; i++) | |
| { | |
| if(arr[i] < pivotValue){ | |
| // if it's already in the correct location, no need to swap | |
| if(i != j) | |
| { | |
| tmp = arr[j]; | |
| arr[j] = arr[i]; | |
| arr[i] = tmp; | |
| } | |
| j += 1; | |
| } | |
| } | |
| // swap the pivot into the correct location | |
| arr[0] = arr[j - 1]; | |
| arr[j - 1] = pivotValue; | |
| } | |
| } |
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