44 lines
1.4 KiB
Go
44 lines
1.4 KiB
Go
package search
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// BinarySearch is an implementation of binary search algorithm.
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// Wikipedia: https://en.wikipedia.org/wiki/Binary_search_algorithm
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//
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// The binary search algorithm begins by comparing the target value to the value
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// of the middle element of the sorted array. If the target value is equal to
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// the middle element's value, then the position is returned and the search is
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// finished. If the target value is less than the middle element's value, then
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// the search continues on the lower half of the array; or if the target value
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// is greater than the middle element's value, then the search continues on the
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// upper half of the array. This process continues, eliminating half of the
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// elements, and comparing the target value to the value of the middle element
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// of the remaining elements - until the target value is either found (and its
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// associated element position is returned), or until the entire array has been
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// searched (and "not found" is returned).
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func BinarySearch(haystack []int, needle int) (pos int, ok bool) {
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if len(haystack) == 0 {
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return 0, false
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}
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if haystack[0] > needle {
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return 0, false
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}
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if haystack[len(haystack)-1] < needle {
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return 0, false
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}
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first := 0
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last := len(haystack)
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for first < last {
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mid := first + (last-first)/2
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if haystack[mid] == needle {
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return mid, true
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} else if haystack[mid] > needle {
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last = mid
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} else {
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first = mid + 1
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}
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}
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return 0, false
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}
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