/**
* Forward declaration of guess API.
* @param {number} num your guess
* @return -1 if num is higher than the picked number
* 1 if num is lower than the picked number
* otherwise return 0
* var guess = function(num) {}
*/
/**
* @param {number} n
* @return {number}
*/
var guessNumber = function(n) {
let start = 1, end = n;
while(true) {
let mid = Math.floor((start + end) / 2);
let myGuess = guess(mid);
if(myGuess === 1) {
start = mid + 1;
} else if(myGuess === -1) {
end = mid - 1
} else {
return mid;
}
}
};