warmup, preparing to give interviews

short_phone_interview_problems/binary_search.py

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+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+def binary_search(array, value):   
+    last, first = len(array), 0
+    
+    while first < last:
+        mid = (last - first)//2
+        item = array[mid]
+        
+        if item == value:
+            return True
+        
+        elif item < value:
+            last = mid
+        
+        else:
+            first = mid 
+    
+    return False
+
+def binary_search_rec(array, value, first=0, last=None):
+    last = last or len(array)
+    if len(array[first:last]) < 1:
+        return False
+    
+    mid = (last - first)//2
+    if array[mid] == value:
+        return True
+    elif array[mid] < value:
+        return binary_search_rec(array, value, first=first, last=mid)
+    else:
+        return binary_search_rec(array, value, first=mid, last=last)
+
+    
+if __name__ == '__main__':    
+    array = [3, 4, 6, 7, 10, 11, 34, 67, 84]
+    value = 6
+    assert(binary_search(array, value) == True)   
+    assert(binary_search_rec(array, value) == True)  
+    value = 8
+    assert(binary_search(array, value) == False)
+    assert(binary_search_rec(array, value) == False)  
+    array = [8]
+    assert(binary_search(array, value) == True)
+    assert(binary_search_rec(array, value) == True)  
+    array = []
+    assert(binary_search(array, value) == False)
+    assert(binary_search_rec(array, value) == False)