Searching and Sorting. Gary Wong. Prerequisite. Time complexity Pseudocode (Recursion). Searching Linear (Sequential) Search Binary Search. Sorting Bubble Sort Merge Sort Quick Sort Counting Sort. Agenda. Linear Search. One by one. Linear Search.
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Gary Wong
One by one...
Not found!
Found!
Chop by half...
1) Initialize boundaries L and R
2) While L is still on the left of R
Smaller? Float! Larger? Sink!
18
9
20
11
77
45
Incorrect order, swap!
Correct order, pass!
Many a little makes a mickle...
List 1:
8
14
22
List 2:
10
13
29
65
Temporary list:
8
8
10
10
13
13
14
14
22
22
29
29
65
65
Combined list:
Merge
10
13
29
65
8
14
22
L
(L+R)/2
(L+R)/2+1
R
mergesort(L,R){
If L is equal to R, done;
Otherwise,
m=(L+R)/2;
mergesort(L,M);
mergesort(M+1,R);
Merge the lists [L,M] and [M+1,R];
}
mergesort(0,6)
mergesort(0,1)
mergesort(2,3)
mergesort(4,5)
mergesort(6,6)
65
10
29
13
14
8
22
mergesort(0,0)
mergesort(1,1)
mergesort(2,2)
mergesort(3,3)
mergesort(4,4)
mergesort(5,5)
mergesort(0,3)
mergesort(4,6)
8
10
10
65
13
10
13
29
13
14
29
65
22
8
8
14
29
14
65
22
10
13
29
65
8
14
22
10
13
8
14
22
65
29
y
Quick Sorta[y] < pivot! shift x, swap!
10
13
29
65
8
14
22
10
13
8
14
22
65
29
quicksort(L,R){
If L is equal to R, done;
Otherwise,
Choose a number as a pivot, say a[p];
Perform pivoting action;
quicksort(L,p-1);
quicksort(p+1,R);
}
No more comparison...
If we have time...
Yummy!