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77 lines
1.8 KiB
C
77 lines
1.8 KiB
C
/*
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Write a recursive function that searches for a target in a sorted array using
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binay search, where the array, its size and the target are given as parameters.
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*/
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#include <limits.h>
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#include <stdio.h>
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#include <assert.h>
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#define DEBUG 1
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#define debug_printf(fmt, ...) \
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do { if (DEBUG) fprintf(stderr, fmt, __VA_ARGS__); } while (0)
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void assert_sorted(int array[], int arraylen) {
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int n = INT_MIN;
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for (int i = 0; i < arraylen; i++) {
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assert(n <= array[i]);
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n = array[i];
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}
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}
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int binsearchr(int array[], int from, int to, int target) {
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int m = from + (to-from)/2;
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debug_printf("from = %d, to = %d, m = %d\n", from, to, m);
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if (to < from)
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return -1;
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if (array[m] == target) {
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return m;
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} else if (array[m] > target) {
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return binsearchr(array, from, m-1, target);
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} else {
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/* array[m] < target */
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return binsearchr(array, m+1, to, target);
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}
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}
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int binsearch(int array[], int arraylen, int target) {
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return binsearchr(array, 0, arraylen-1, target);
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}
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int main(void) {
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int a[43] = {
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912, 1204, 1761, 2143, 3691,
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5150, 5249, 6864, 6871, 6902,
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9567, 9703, 10411, 10686, 13501,
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14378, 16249, 17393, 17911, 18614,
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19284, 19595, 19960, 20052, 20702,
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21090, 22277, 22624, 24634, 24877,
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25367, 25586, 26706, 26720, 26958,
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27478, 28269, 29142, 30630, 30804,
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31984, 32398, 32588
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};
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assert_sorted(a, 43);
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assert(binsearch(a, 43, 912) == 0);
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assert(binsearch(a, 43, 3691) == 4);
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assert(binsearch(a, 43, 32588) == 42);
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assert(binsearch(a, 43, 12345) == -1);
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int b[2] = { 23, 42 };
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assert_sorted(b, 2);
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assert(binsearch(b, 2, 23) == 0);
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assert(binsearch(b, 2, 42) == 1);
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assert(binsearch(b, 2, 5) == -1);
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assert(binsearch(b, 2, 99) == -1);
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int c[1] = { 0 };
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assert_sorted(c, 1);
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assert(binsearch(c, 1, 0) == 0);
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assert(binsearch(c, 1, 1) == -1);
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}
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