binary search 问题

dan123

In the binary search program on page 112, why did we write mid = beg + (end - beg) / 2; instead of mid = (beg + end) /2;?

1. // text must be sorted
   
2. // beg and end will denote the range we're searching
   
3. auto beg = text.begin(), end = text.end();
   
4. auto mid = text.begin() + (end - beg)/2; // original midpoint
   
5. // while there are still elements to look at and we haven't yet found sought
   
6. while (mid != end && *mid != sought) {
   
7. if (sought < *mid) // is the element we want in the first half?
   
8. end = mid; // if so, adjust the range to ignore the second
   
9. half
   
10. else // the element we want is in the second half
    
11. beg = mid + 1; // start looking with the element just after mid
    
12. mid = beg + (end - beg)/2; // new midpoint
    
13. }

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shuofxz

Isn't the same?

beg + (end - beg) / 2
= beg + end/2 - beg / 2
= beg / 2 + end/2
= (beg + end) /2