374. Guess Number Higher or Lower

Guess Number Higher or Lower

Problem Description

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 will tell you whether the number I picked is higher or lower than your guess.

You call a pre-defined API int guess(int num), which returns three possible results:

• -1: Your guess is higher than the number I picked (i.e. num > pick).
• 1: Your guess is lower than the number I picked (i.e. num < pick).
• 0: your guess is equal to the number I picked (i.e. num == pick).

Return the number that I picked.

 

Example 1:

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

Example 2:

Input: n = 1, pick = 1
Output: 1

Example 3:

Input: n = 2, pick = 1
Output: 1

 

Constraints:

• 1 <= n <= 231 - 1
• 1 <= pick <= n

Approach) Binary Search

var guessNumber = function(n) { 
    return (function foo(start, end) {
        let num = ((end + start)/2)
        let g = guess(num);
        if (g === -1) {
            return foo(start, num-1)
        } else if (g === 1) {
            return foo(num+1, end)
        } else {
            return num;
        }
    })(1, n);
};

Approach) Recursion

var guessNumber = function(n) {
    const helperRecursive = (low, high) => {
        const mid = Math.floor((low+high)/2);        
        
        if(guess(mid) === 0) return mid;
        if(guess(mid) === 1) return helperRecursive(mid+1,high);
        if(guess(mid) === -1) return helperRecursive(low,mid-1);
        
    }
    
    return helperRecursive(0,n);
};

Conclusion

That’s all folks! In this post, we solved LeetCode problem 374. Guess Number Higher or Lower

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