55 lines
1.4 KiB
C
55 lines
1.4 KiB
C
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#include <stdio.h>
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#include <string.h>
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int partition(int* a, int low, int high)
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{
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int left = low;
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int pivotIdx = low + (high - low)/2;
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int pivot = a[pivotIdx];
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a[pivotIdx] = a[high];
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a[high] = pivot;
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pivotIdx = high;
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int partitionIdx = low;
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while (left < high)
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{
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if (a[left] < pivot)
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{
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int tmp = a[left];
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a[left] = a[partitionIdx];
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a[partitionIdx] = tmp;
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++partitionIdx;
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}
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++left;
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}
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a[pivotIdx] = a[partitionIdx];
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a[partitionIdx] = pivot;
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return partitionIdx;
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}
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int quickselect(int* a, int low, int high, int k)
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{
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if (low == high)
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return a[low];
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int pivotIdx = partition(a, low, high);
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int sizeOfLeftSubArray = pivotIdx - low + 1;
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if (sizeOfLeftSubArray > k)
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{
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return quickselect(a, low, pivotIdx-1, k);
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}
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else if (sizeOfLeftSubArray < k)
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{
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return quickselect(a, pivotIdx+1, high, k-sizeOfLeftSubArray);
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}
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else
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{
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return a[pivotIdx];
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}
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}
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int main()
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{
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int arr[] = {4, 5, 22, 49, 64, 43, 32, 323, 78, 90};
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int k;
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printf("\nEnter the number 'k' to find the 'kth' largest element: ");
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scanf("%d", &k);
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printf("\nKth largest element is %d", quickselect(arr, 0, 9, k));
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return 0;
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}
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