55 lines
1.6 KiB
Go
55 lines
1.6 KiB
Go
package binary
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/* ---------------------------------------------------------------- *
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* IMPORTS
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* ---------------------------------------------------------------- */
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import (
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"ads/internal/core/logging"
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"ads/internal/core/metrics"
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)
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/* ---------------------------------------------------------------- *
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* GLOBAL VARIABLES/CONSTANTS
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* ---------------------------------------------------------------- */
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//
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/* ---------------------------------------------------------------- *
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* ALGORITHM binary search
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* ---------------------------------------------------------------- */
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/*
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Inputs: L = Liste von Zahlen, x = Zahl.
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Annahme: L sei aufsteigend sortiert.
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Outputs: Position von x in L, sonst −1 wenn x nicht in L.
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*/
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func BinarySearch(L []int, x int) int {
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if len(L) == 0 {
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logging.Debug("x nicht in L.")
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return -1
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}
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metrics.AddTimeCost()
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m := int(len(L) / 2)
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if L[m] == x {
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logging.Debug("Suche in %v .. %v; m = %v; L[m] = x ==> Element gefunden.", 0, len(L)-1, m)
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return m
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} else if len(L) == 1 {
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logging.Debug("L enthält 1 Element; L[m] =/= x; ==> x nicht in L.")
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return -1
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} else if x < L[m] {
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logging.Debug("Suche in %v .. %v; m = %v; L[m] = %v > x ==> Suche in linker Hälfte fortsetzen.", 0, len(L)-1, m, L[m])
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index := BinarySearch(L[:m], x)
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return index
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} else { // } else if x > L[m] {
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logging.Debug("Suche in %v .. %v; m = %v; L[m] = %v < x ==> Suche in rechter Hälfte fortsetzen.", 0, len(L)-1, m, L[m])
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index := BinarySearch(L[m+1:], x)
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if index == -1 {
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return -1 // wenn nicht gefunden
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}
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return index + (m + 1) // NOTE: muss Indexwert kompensieren
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}
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}
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