# Binary Search

#### Pseudocode

Here's the pseudocode for binary search, modified for searching in an array. The inputs are the array, which we call `array`; the number `n` of elements in `array`; and `target`, the number being searched for. The output is the index in `array` of `target`:

Here is modified pseudocode for binary search that handles the case in which the target number is not present:

1. Let `min = 0` and `max = n-1`.
2. If `max < min`, then stop: `target` is not present in `array`. Return `-1`.
3. Compute `guess` as the average of `max` and `min`, rounded down (so that it is an integer).
4. If `array[guess]` equals `target`, then stop. You found it! Return `guess`.
5. If the guess was too low, that is, `array[guess] < target`, then set `min = guess + 1`.
6. Otherwise, the guess was too high. Set `max = guess - 1`.
7. Go back to step 2.

```python
import math

primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]


def doSearch(array, target_value):
    min_value = 0
    max_value = len(array) - 1

    while min_value <= max_value:
        guess = int(math.floor((max_value + min_value) / 2))
        if array[guess] == target_value:
            return guess
        elif array[guess] < target_value:
            min_value = guess + 1
        else:
            max_value = guess - 1

    return -1;


target = 73
print(doSearch(primes, target))
```


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