How to find the maximum number in an array that occurs only once?

To find the maximum number in an array that occurs exactly once, you can follow these steps:

1. Count the occurrences of each number (for example, using a dictionary/hash table).
2. Filter out the numbers that occur only once.
3. Find the maximum among these numbers.

Example in Go:

package main

import (
    "fmt"
)

func maxUnique(nums []int) (int, bool) {
    counts := make(map[int]int)
    for _, num := range nums {
        counts[num]++
    }

    maxVal := 0
    found := false
    for num, count := range counts {
        if count == 1 {
            if !found || num > maxVal {
                maxVal = num
                found = true
            }
        }
    }
    return maxVal, found
}

func main() {
    arr := []int{2, 3, 5, 3, 7, 5, 8}
    if maxNum, ok := maxUnique(arr); ok {
        fmt.Println("Maximum number occurring exactly once:", maxNum)
    } else {
        fmt.Println("No numbers occur exactly once")
    }
}

If there are no numbers that occur exactly once in the array, the function returns false as the second parameter.