No.253 ロウソクの長さ on CommonLisp | Codetter（こーどったー）

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;https://yukicoder.me/problems/no/253
(let (
    (numMin 10)
    (numMax 1000000001)
)
    (loop for turn from 0 do
        (let ((chkNum (if(= 0 turn) 100 (floor(/(+ numMin numMax) 2)))))
            (format t "? ~d~%" chkNum)(force-output)
            (let ((chk (read-line)))
                (if(string= "1" chk) (setf numMin chkNum)
                (if(string= "-1" chk) (setf numMax chkNum)
                (progn
                    (format t "! ~d~%" (+ chkNum turn))(force-output)
                    (return)
                )))
                (when(< 0 numMin) (decf numMin))
                (decf numMax)
            )
        )
    )
)
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