Lectures12-part-09-algorithms-1

Nowsorttheleftrightusing quicksortmethod quicksort

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Unformatted text preview: n2­n)/2 = n2/2 ­ n/2 ≤ n2/2 A presidential message Insertion Sort Insertion Sort (typical method for sorting playing cards in hand) Insert first Insert next into proper place Insert next into proper place etc. Insertion Sort Insertion Sort FOR i = 1 to n /* Insert M(i) into correct place in new list T() { j = 1 /* Start looking at position T(1) WHILE M(i) < T(j) { j = j+1 } /* AHA! M(i) belongs right after T(j) slide T(j+1), T(j+2), … over to T(j+2), T(j+3)… T(j+1) = M(i) } where slide is a separate “procedure” that we have written. Running Times Running Times Insertion Sort: 1 + 2 + 3 + 4 … + n­1 ≤ n2/2 (see previous analysis) Quick Sort Quick Sort A very fast method in practice Used often, especially with large data sets Quick Sort Quick Sort 15 9 4 2 78 36 3 1 2 4 59 78 6 Pick a “pivot’ at random Compare each element to the pivot, placing it to left or right Pivot is in correct place. Now sort the left, right using Quick Sort method….. Quick Sort Quick Sort 3 1 2 4 59 78 6 Pick a pivot at random Compare each element to the pivot, placing it to left o...
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