Алгоритмы - Введение

 
 def binary_search(list, item):
   # low and high keep track of which part of the list you'll search in.
   low = 0
   high = len(list) - 1
 
   # While you haven't narrowed it down to one element ...
   while low <= high:
     # ... check the middle element
     mid = (low + high) // 2
     guess = list[mid]
     # Found the item.
     if guess == item:
       return mid
     # The guess was too high.
     if guess > item:
       high = mid - 1
     # The guess was too low.
     else:
       low = mid + 1
 
   # Item doesn't exist
   return None
 
 my_list = [1, 3, 5, 7, 9]
 print(binary_search(my_list, 3)) # => 1
 
 # 'None' means nil in Python. We use to indicate that the item wasn't found.
 print(binary_search(my_list, -1)) # => None
 
 

 
 package main
 
 import "fmt"
 
 func checkBin(list []int, i int) bool {
 	low := 0
 	high := len(list) - 1
 	for low <= high {
 		mid := (low + high) / 2
 		if list[mid] == i {
 			return true
 		}
 		if list[mid] < i {
 			low = mid + 1
 		} else {
 			high = mid - 1
 		}
 	}
 	return false
 }
 
 func main() {
 	fmt.Println(checkBin([]int{1, 2, 3, 4, 5}, 1))  // true
 	fmt.Println(checkBin([]int{1, 2, 3, 4, 5}, -1)) //false
 }
 
 

 
 #include <stdio.h>
 
 int binarySearch(int[], int, int);
 
 int main()
 {
     int myList[] = {1, 3, 5, 7, 9};
     int len = sizeof(myList) / sizeof(myList[0]);
 
     printf("%d\n", binarySearch(myList, 3, len));  // 1
     printf("%d\n", binarySearch(myList, -1, len)); //-1
     return 0;
 }
 
 int binarySearch(int list[], int item, int len)
 {
     int low = 0;
     int high = len;
     while (low <= high)
     {
         int mid = (low + high)/2; 
         int guess = list[mid];
 
         if (guess == item)
         {
             return mid;
         }
         else if (guess > item)
         {
             high = mid - 1;
         }
         else
         {
             low = mid + 1;
         }
     }
     return -1; //number not found
 }