Find K Pairs with Smallest Sums

Desicription

We are playing the Guess Game. The game is as follows:

I pick a number from 1 to n. You have to guess which number I picked.

Every time you guess wrong, I’ll tell you whether the number is higher or lower.

You call a pre-defined API guess(int num) which returns 3 possible results (-1, 1, or 0):

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-1 : My number is lower
1 : My number is higher
0 : Congrats! You got it!

Example :

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Input: n = 10, pick = 6
Output: 6

Solution

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// Forward declaration of guess API.
// @param num, your guess
// @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
int guess(int num);

class Solution {
public:
int guessNumber(int n) {
long long left = 1;
long long right = n;
while(true) {
long long mid = (left + right) >> 1;
if(guess(mid) == 0) {
return mid;
} else if(guess(mid) == 1) {
left = mid + 1;
} else {
right = mid - 1;
}
}
}
};