Design a stack with max frequency element operation

// Create an empty object to store frequencies
let freq = {};

// Create an empty array to store values along with their frequencies and positions
let arr = [];

// Create a variable to keep track of the position of the last added element
let pos = 0;

// Function to add an element to the array and update its frequency
function push(x) {

// If the frequency of the element is not already in the object, add it
if (freq[x] === undefined) freq[x] = 0;

// Increase the frequency of the element and store its frequency, position and value in the array
freq[x]++;
arr.push([freq[x], ++pos, x]);
}

// Function to remove the element with the highest frequency and position from the array
function pop() {

// Create variables to store the maximum frequency and position of elements in the array
let maxIdx = -1;
let maxVal = -1;

// Loop through the array to find the element with the highest frequency and position
for (let i = 0; i < arr.length; i++) {
let [freq, idx, val] = arr[i];
if (freq > maxVal || (freq == maxVal && idx > maxIdx)) {
maxIdx = idx;
maxVal = freq;
}
}

// Loop through the array again to find the index of the element with the highest frequency and position
let idx = -1;
for (let i = 0; i < arr.length; i++) {
if (arr[i][1] == maxIdx) {
idx = i;
break;
}
}

// Store the frequency, position and value of the element to be removed
let [freq, pos, x] = arr[idx];

// Decrease the frequency of the element in the object
freq--;

// If the frequency of the element becomes zero, delete it from the object
if (freq == 0) delete freq[x];
else freq[x] = freq;

// Remove the element from the array
arr.splice(idx, 1);

// Return the value of the removed element
return x;
}

// Add some elements to the array
push(4);
push(6);
push(7);
push(6);
push(8);

// Remove and print the two elements with the highest frequency and position
console.log(pop());
console.log(pop());

<script>

// Javascript implementation of the approach

// freqMap is to map element to its frequency
var freqMap = new Map();

// setMap is to map frequency to the
// element list with this frequency
var setMap = new Map();

// Variable which stores maximum frequency
// of the stack element
var maxfreq = 0;

// Function to insert x in the stack
function push(x)
{

    // Frequency of x
    if(!freqMap.has(x))
        freqMap.set(x, 1)
    else
        freqMap.set(x, freqMap.get(x)+1)
    
    var freq = freqMap.get(x)

    // Mapping of x with its frequency
    freqMap.set(x, freq);

    // Update maxfreq variable
    if (freq > maxfreq)
        maxfreq = freq;

    // Map element to its frequency list
    // If given frequency list doesn't exist
    // make a new list of the required frequency
    if(!setMap.has(freq))
    {
        setMap.set(freq, [x])
    }
    else
    {
        var tmp = setMap.get(freq);
        tmp.push(x);
        setMap.set(freq, tmp);
    }
}

// Function to remove maximum frequency element
function pop()
{

    // Remove element from setMap
    // from maximum frequency list
    var tmp = setMap.get(maxfreq);
    var top = tmp[tmp.length-1];
    tmp.pop();
    setMap.set(maxfreq, tmp);

    // Decrement the frequency of the popped element
    if(freqMap.has(top))
        freqMap.set(top, freqMap.get(top)-1)

    // If whole list is popped
    // then decrement the maxfreq
    if (setMap.get(maxfreq).length == 0)
        maxfreq--;
    return top;
}

// Driver code
// Push elements to the stack
push(4);
push(6);
push(7);
push(6);
push(8);

// Pop elements
document.write( (pop()) + "<br>");
document.write( (pop()));

// This code is contributed by itsok.
</script>