1 linear and binary search instructor: mainak chaudhuri mainakc@cse.iitk.ac.in
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Linear and Binary Search
Instructor: Mainak Chaudhurimainakc@cse.iitk.ac.in
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Linear searchclass LinearAndBinarySearch { public static void main (String arg[]) { int size = 20, key = 23; int array[] = new int[size];
Initialize (array, size); // not shown PrintArray (array, size); // not shown System.out.println (“Linear search result:
” + LinearSearch (array, key)); System.out.println (“Binary search
result: ” + BinarySearch (array, 0, size-1, key));
}
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Linear search public static int LinearSearch (int
array[], int key) { int i;
for (i=0;i<array.length;i++) { if (array[i] == key) { return i; } } return -1; }
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Binary search public static int BinarySearch (int array[],
int start, int end, int key) { // Pre-condition: array is sorted // Caution: binary search does not work // on unsorted arrays. int mid; if (start > end) return -1; if (start == end) { if (key == array[start]) return start; else return -1; } // continued in next slide
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Binary search mid = (start + end)/2; if (key == array[mid]) return mid; else if (key < array[mid]) { return BinarySearch (array, start, mid-1,
key); } else { return BinarySearch (array, mid+1, end,
key); } }} // end class
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Run time analysis• Linear search in the worst case
requires n comparisons• Binary search in the worst case
requires O(log n) comparisons– Solution to T(n) = T(n/2) + O(1)– Remember that binary search can be
applied to sorted arrays only
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