cpts121-9-1 - 1 C ptS 121 L9-1 10/19/09 Pro f. C hris...

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Unformatted text preview: 1 C ptS 121 L9-1 10/19/09 Pro f. C hris Hundha us e n CptS 121 Fall 09 Lecture 9-1 HK Chapter 8: Arrays Lecture Outline I. Array Sorting II. Array Searching 2 C ptS 121 L9-1 10/19/09 Pro f. C hris Hundha us e n Array Sorting Lots of motivating problems- Print out a class list in alphabetical order- Order finish times in a race to determine who placed- Make look-up easier (preparation for binary search) 3 C ptS 121 L9-1 10/19/09 Pro f. C hris Hundha us e n Array Sorting (cont.) Selection Sort Input: a list of numbers Output: a list of the same numbers in ascending order Intuition: Build up a sorted list by successively finding smallest elements in unsorted portion of array, and placing those values at end of sorted portion of list Method: - Set marker that divides sorted and unsorted sections of list to the beginning of the list- While the unsorted section of the list is larger than one element Call upon Find_Smallest helper function to find index of smallest value in unsorted section of list Swap value indexed by marker in with smallest value in unsorted section of list Move "sorted/unsorted" marker right one position 4 CptS 121 L9-1 10/19/09 Prof. Chris Hundhausen Array Sorting (cont.) C adaptation of selection sort (compiled and tested!) void selection_sort(int values, int num_values) { int i, index_of_smallest, temp; for (i = 0; i < num_values - 1; ++i) { /* Find the index of the smallest element in unsorted list... */ index_of_smallest = find_smallest(values,i,num_values-1); /* Swap the smallest value in the subarray i+1 .. num_values - 1 with the value i, thereby putting into place the ith element. */ temp = values[i]; values[i] = values[index_of_smallest]; values[index_of_smallest] = temp; } } int find_smallest(int values, int low, int high) { int smallest_index, i; smallest_index = low; for (i = low + 1; i <= high; i++) if (values[i] < values[smallest_index]) smallest_index = i; return smallest_index; } 5 C ptS 121 L9-1 10/19/09 Pro f. C hris Hundha us e n Array Sorting (cont.) Insertion Sort Input: a list of numbers Output: a list of the same numbers in ascending order Intuition: Successively insert first item in unsorted portion of list into sorted portion of list Method: - Set marker that divides sorted and unsorted sections of...
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cpts121-9-1 - 1 C ptS 121 L9-1 10/19/09 Pro f. C hris...

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