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Computer Science Introduction to Algorithms Algorithms in Code Binary Search in Code

Leo Yun Tao
Leo Yun Tao
15,956 Points
Posted by Leo Yun Tao
Leo Yun Tao
15,956 Points

Why must the midPoint + 1 or -1

I do not understand why must we minus 1 or add 1 when we are setting the first and the last to be the midPoint?

1 Answer

Dale Severude
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Dale Severude
Full Stack JavaScript Techdegree Graduate 71,349 Points
Dale Severude
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Dale Severude
Full Stack JavaScript Techdegree Graduate 71,349 Points

Hi Leo,

The first condition of our if statement tests if the midpoint is equal to our target. If so, then we are done and the function returns the correct target.

If the midpoint did not equal our target, then we know that we don't need to use the current midpoint anymore because it has already been tested as false. Then it is a simple matter of either adding or subtracting one to our midpoint to begin to use a new untested value as part of our new range of values for the next loop.