Leetcode 1133

Here are two ways to solve this solution:

One way is to use an array of size 1001 which we call h (1001 because in the notes it says 0 <= A[i] <= 1000) and add one to h[A[i]]. Now we can see that the array will be sorted because we add the number of numbers to h. So all we have to do is iterate through h backward and check whether the value of h[i] == 1. If so, return i. If there are no unique numbers, we can return -1.

The other way is to use a map. We can first iterate through A and add one to the value of A. Then we can iterate through the map and look for all unique numbers. If the current number is greater than the max, we can re-assign the max to the number. After all of that, return the max value.

Using an Array:

func largestUniqueNumber(A []int) int {
    h := make([]int, 1001)

    for _, i := range A {
        h[i]++
    }
    for i := 1000; i >= 0; i-- {
        if h[i] == 1 {
            return i
        }
    }
    return -1
}

Using a Map

func largestUniqueNumber(A []int) int {
    h := make(map[int]int)
    number := -1

    for _, i := range A {
        h[i]++
    }

    for i, i2 := range h {
        if i2 == 1 && i > number {
            number = i
        }
    }

    return number
}