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I am trying to write a function to find the majority element in kotlin but when I compile the code I get variable expected error on the following line

                   map[key]?.let{ value->
Below is the function which I am trying to run. I am new to Kotlin and not sure why I am getting this error.
fun majorityElement(nums: IntArray): Int {
        HashMap<Int,Int>().let{ map ->
                nums.forEach{ key->        
                   map[key]?.let{ value->
                        map[key]=value+1
                    }?:map[key]=1
                map.forEach{entry->
                    if(entry.value>nums.size/2){
                        return entry.key
        return -1
Here the expression is parsed not the way you might expect. map[key]?.let { ... } ?: map[key] becomes an l-value of the assignment operator and 1 becomes an r-value.
The l-value of an assignment must be something that you can assign a value to, i.e. a variable, a property, an indexer, like map[key] =, but here it is a complex expression 
 map[key]?.let { ... } ?: map[key].
If you want to execute assignment only when map[key] is null, you can wrap that statement in run function: 
map[key]?.let { ... } ?: run { map[key] = 1 }
Perhaps it would be more clear to rewrite this block the following way:
// get value associated with key or 0 if there is none.
map[key] = map.getOrElse(key, { 0 }) + 1
Looking from a higher perspective, it seems that you need to count the occurrences of numbers in an array of ints. For that case a more high-level approach with groupingBy and eachCount functions can be used:
val map = nums.asList().groupingBy { it }.eachCount()
// then find the majority in this map
        
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