ads1_2021/code/algorithms/search/binary.py

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Python
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# IMPORTS
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
from local.maths import *;
from local.typing import *;
from code.core.log import *;
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# GLOBAL VARIABLES/CONSTANTS
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# ALGORITHM binary search
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
def BinarySearch(L: List[int], x: int) -> int:
'''
Inputs: L = Liste von Zahlen, x = Zahl.
Annahme: L sei aufsteigend sortiert.
Outputs: Position von x in L, sonst 1 wenn x nicht in L.
'''
if len(L) == 0:
logDebug('x nicht in L');
return -1;
AddToCounter();
m = math.floor(len(L)/2);
if L[m] == x:
logDebug('x in Position m gefunden');
return m;
elif x < L[m]:
logDebug('Suche in L[0], L[1], ..., L[m] fortsetzen, m = {}.'.format(m));
index = BinarySearch(L[:m], x);
return index;
else: # x > L[m]
logDebug('Suche in L[m+1], L[m+2], ..., L[len(L)-1] fortsetzen, m = {}.'.format(m));
index = BinarySearch(L[m+1:], x);
return (m + 1) + index; # NOTE: muss Indexwert kompensieren