Start learning free

LESSON 143 OF 338 · LOOPS & GLOBAL VARIABLES

Maximum Value in an Array in Go

Practice Read the full explanation

Given an array of integers, return the maximum value from the array.

Example:

Input: nums = [2, 7, 11, 8, 11, 8, 3, 11]
Output: 11
Explanation: The maximum value is 11

Note:

Do not use builtin functions such as max(), it would defy the purpose of the challenge. Write the whole code yourself.

STEP 1 OF 4
    Ctrl + Enter to check

    GO · LOOPS & GLOBAL VARIABLES

    Max In Array in Go, explained

    Problem overview

    The function maxInArray receives a slice of integers, nums, and returns the largest value in it. For [2, 7, 11, 8, 11, 8, 3, 11] the answer is 11. The value 11 appears three times, which doesn't matter: the function returns the value, not a position or a count.

    Approach

    Keep a variable that holds the largest value seen so far, and look at every element once. Whenever an element is larger than the stored one, replace it. After the last element, the variable holds the maximum of the whole slice.

    The choice of starting value matters. The tempting start is 0, but it fails when every number is negative: for [-5, -2, -9], a start of 0 is larger than all of them and the function would return 0, a number that isn't in the slice. Starting with the first element avoids this, because the answer is always an element of the slice and the first element is a valid candidate to begin with.

    Step by step

    1. Initialize maxVal with nums[0] using :=. It becomes an int holding the first element.
    2. Loop over the values. for _, num := range nums gives each element in turn as num. The blank identifier _ discards the index, since Go does not allow unused variables.
    3. Update the maximum. Inside the loop, set maxVal to the larger of maxVal and num. Go provides a built-in max function for this, so the assignment is a single line, and maxVal always holds the largest value seen so far.
    4. Return maxVal after the loop.

    The solution in Go

    func maxInArray(nums []int) int {
    maxVal := nums[0]
    for _, num := range nums {
        maxVal = max(maxVal, num)
    }
    return maxVal
}

    The Go details worth knowing:

    • The built-in max. Go 1.21 added the built-ins min and max. They accept two or more arguments of the same ordered type, so max(3, 8) is 8. Before that version, Go had no such function in the standard language and people wrote the comparison themselves.
    • The same thing without the built-in. If you prefer to spell it out, replace the assignment with an if: 
      if num > maxVal {
    maxVal = num
}
      It gives the same result for every input. For [2, 7, 11, 8, 11, 8, 3, 11] it returns 11, and for [-5, -2, -9] it returns -2.
    • The first element is compared with itself. The loop starts at index 0, so the first pass compares nums[0] with nums[0]. This is harmless. A loop that starts at index 1 would skip the useless comparison, but it needs the index and a three-part for, and the saving is negligible.
    • No ternary operator. Go has no a > b ? a : b, which is one reason the built-in max and the plain if are the two ways to write this.

    Complexity

    Time: O(n). The loop looks at each of the n elements once, and each comparison takes constant time. Any correct solution has to read every element, because the largest one could be anywhere.

    Space: O(1). The function stores only maxVal and the loop variable.

    Edge cases and common mistakes

    • All negative numbers. [-5, -2, -9] returns -2. Starting maxVal at 0 would return 0 instead.
    • A single element. [42] returns 42.
    • An empty slice. nums[0] does not exist, so the function stops the program with a run-time panic, index out of range [0] with length 0. This solution assumes at least one element. If empty input were possible, check len(nums) == 0 first and decide what to return.
    • Duplicated maxima. [11, 7, 11] returns 11. Nothing special is needed.
    • Returning inside the loop. The function would give up after the first element.
    • Using a tiny constant as the start. Starting from a fixed number such as -1000 works only while the data stays above it. The first element works for every input.

    Testing

    • []int{2, 7, 11, 8, 11, 8, 3, 11} gives 11.
    • []int{-5, -2, -9} gives -2.
    • []int{42} gives 42.
    • []int{1, 2, 3} gives 3.
    Keep going with GoAbout 340 step-by-step lessons, from your first line of code to coding interviews. Free to start.
    Start learning free