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Quick sort

Quick sort. void quick_sort ( int a[], int l, int r) { int i, j,v, t; if (r>l) { v=a[r]; //L’elemento “pivot” è quello più a dx i=l-1; j=r; // i scorre da sx a dx; j da dx a sx for (;;) { while ( a[++i]<v); while ( a[--j]>v)if(j==l) break; if (i>=j) break;

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Quick sort

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  1. Quick sort void quick_sort (int a[],int l, int r) { int i, j,v, t; if (r>l) { v=a[r];//L’elemento “pivot” è quello più a dx i=l-1; j=r;// i scorre da sx a dx; j da dx a sx for (;;) { while ( a[++i]<v); while ( a[--j]>v)if(j==l) break; if (i>=j) break; t=a[i]; a[i]=a[j]; a[j]=t;//Scambia gli//elementi i e j } t=a[i]; a[i]=a[r]; a[r]=t;//Sistema l’elemento “pivot” quick_sort (a, l, i-1); quick_sort (a, i+1, r); } }

  2. Quick sort i = > j ? NO! Scambio a[i] e a[j] i = > j Scambio a[i] e a[r] r > l l r 3 5 2 7 4 4 1 1 1 5 7 pivot i j a[j] > v? NO a[i] < v 1 4 NO a[j] > v 4 temp v

  3. chiamata ricorsiva quick_sort (a, l, i-1); l i-1 3 1 2 quick_sort (a, i+1, r); i+1 r 7 5

  4. i = > j ? NO! Scambio a[i] e a[j] r > l l r 3 1 2 1 3 2 3 while ( a[++i]<v); j i pivot while ( a[--j]>v); i = > j ? SI! Scambio a[i] e a[r] 1 2 2 temp v

  5. chiamata ricorsiva quick_sort (a, l, i-1); Valore uguale FINE quick_sort (a, i+1, r); Valore uguale FINE

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