CodeWars - Delete occurrences of an element if it occurs more than n …

…times

deleteNth.js

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+/**
+ * Enough is enough!
+*   Alice and Bob were on a holiday. Both of them took many pictures of the places they've been, 
+*   and now they want to show Charlie their entire collection. However, Charlie doesn't like this sessions, 
+*   since the motive usually repeats. He isn't fond of seeing the Eiffel tower 40 times. He tells them that 
+*   he will only sit during the session if they show the same motive at most N times. Luckily, Alice and Bob
+*   are able to encode the motive as a number. Can you help them to remove numbers such that their list
+*   contains each number only up to N times, without changing the order?
+
+ *  Task
+*     Given a list lst and a number N, create a new list that contains each number of lst at most N times 
+*     without reordering. For example if N = 2, and the input is [1,2,3,1,2,1,2,3], you take [1,2,3,1,2], 
+*     drop the next [1,2] since this would lead to 1 and 2 being in the result 3 times, and then take 3,
+*     which leads to [1,2,3,1,2,3].
+
+*   Example
+*     deleteNth ([1,1,1,1],2) // return [1,1]
+*     deleteNth ([20,37,20,21],1) // return [20,37,21]
+*/
+
+const _updateHashMap = (hashMap, val) => {
+  if (hashMap.has(val)) {
+     let value = hashMap.get(val)
+     hashMap.set(val, value+1)
+   } else {
+     hashMap.set(val, 1)
+   }
+ }
+
+ function deleteNth(arr,n){
+   // ...
+   const hashMap = new Map()
+   const newArray = []
+   return arr.filter(a=>{
+     _updateHashMap(hashMap, a)
+     if (hashMap.get(a) <= n) {
+       return a
+     }
+   })
+   return newArray
+ }