在Golang中使用地图

Question

I am new to Go and doing a few exercises. One of them is to sort the numbers in an array by frequency, from most to least frequent.

Example: 
Input: [2, 2, 5, 7, 4, 4, 4, 7, 2]
Output: [2, 4, 7, 5]

Note that [4, 2, 7, 5] would also be correct, since 4 and 2 have the same frequency.

For this purpose I am converting the array into a value value map, which here would look like this: [2:3][4:3][7:2][5:1] (2 and 3 have freq. of 3, 7 has the freq of 2,... )

Afterwards I would like to simply loop through the map and output the keys ordered by value. For that I use the following code, which apparently does not work. Why?

count := 0
max := -1

// break loop, if map is empty
for i := 0; i < 1; i-- {
    if len(m) == 0 {
        break
    }

    max = -1

    // get key of biggest value
    for k, v := range m {
        if v > max {
            max = k
        }
    }
    // res (for result) is a slice of integers
    res[count] = max
    // remove key-value-pair from map
    delete(m, max)
    count++
}
return res

Please keep in mind that this is an exercise. I am very sure there are much better, build in ways to do this.

Answer 1

Your 'max' variable is meant to keep track of the maximum frequency seen so far. However when you do 'max = k' you're assigning a key.

You need to keep track of the maximum frequency and the key associated with that frequency in separate variables.

...
for k, v := range m {
    if v > maxFreq {
        maxFreq = v
        mostFrequentKey = k
    }
}
// res (for result) is a slice of integers
res[count] = mostFrequentKey
// remove key-value-pair from map
delete(m, mostFrequentKey)
count++
...