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method

# bsearch v2_5_5 - Show latest stable - 0 notes - Class: Array
`bsearch()` public

By using binary search, finds a value from this array which meets the given condition in O(log n) where n is the size of the array.

You can use this method in two modes: a find-minimum mode and a find-any mode. In either case, the elements of the array must be monotone (or sorted) with respect to the block.

In find-minimum mode (this is a good choice for typical use cases), the block must always return true or false, and there must be an index i (0 <= i <= ary.size) so that:

• the block returns false for any element whose index is less than i, and

• the block returns true for any element whose index is greater than or equal to i.

This method returns the i-th element. If i is equal to ary.size, it returns nil.

```ary = [0, 4, 7, 10, 12]
ary.bsearch {|x| x >=   4 } #=> 4
ary.bsearch {|x| x >=   6 } #=> 7
ary.bsearch {|x| x >=  -1 } #=> 0
ary.bsearch {|x| x >= 100 } #=> nil
```

In find-any mode (this behaves like libc’s bsearch(3)), the block must always return a number, and there must be two indices i and j (0 <= i <= j <= ary.size) so that:

• the block returns a positive number for ary[k] if 0 <= k < i,

• the block returns zero for ary[k] if i <= k < j, and

• the block returns a negative number for ary[k] if j <= k < ary.size.

Under this condition, this method returns any element whose index is within i…j. If i is equal to j (i.e., there is no element that satisfies the block), this method returns nil.

```ary = [0, 4, 7, 10, 12]
# try to find v such that 4 <= v < 8
ary.bsearch {|x| 1 - x / 4 } #=> 4 or 7
# try to find v such that 8 <= v < 10
ary.bsearch {|x| 4 - x / 2 } #=> nil
```

You must not mix the two modes at a time; the block must always return either true/false, or always return a number. It is undefined which value is actually picked up at each iteration.

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