/*
Goal:
- Select N random values that appear exactly once in the array.
- The array includes duplicates, but only values with frequency = 1
are eligible for selection.
Approach:
1. Count frequencies using a Map.
2. Collect values that appear exactly once.
3. Shuffle the unique list.
4. Take the first N values.
5. Return them and print them.
Notes:
- Uses modern JavaScript (ES6+).
- Uses expressive, structured functions.
*/
//---------------------------------------------------------------
// Build a frequency map: value -> count
//---------------------------------------------------------------
function buildFrequencyMap(data) {
const freq = new Map();
for (const value of data) {
freq.set(value, (freq.get(value) || 0) + 1);
}
return freq;
}
//---------------------------------------------------------------
// Collect values that appear exactly once
//---------------------------------------------------------------
function collectGloballyUniqueValues(data, freq) {
return data.filter(value => freq.get(value) === 1);
}
//---------------------------------------------------------------
// Randomly select N values from the unique list
//---------------------------------------------------------------
function selectRandomUnique(unique, N) {
if (N > unique.length) {
N = unique.length; // clamp
}
// Shuffle using Fisher–Yates
const temp = [...unique];
for (let i = temp.length - 1; i > 0; i--) {
const j = Math.floor(Math.random() * (i + 1));
[temp[i], temp[j]] = [temp[j], temp[i]];
}
return temp.slice(0, N);
}
//---------------------------------------------------------------
// Print helper
//---------------------------------------------------------------
function printList(list) {
console.log(list.join(" "));
}
//---------------------------------------------------------------
// Main program
//---------------------------------------------------------------
(function main() {
// Example array with duplicates
const data = [
5, 12, 5, 19, 5, 33, 19, 5, 8, 8, 8, 59, 61, 17, 3, 5, 3, 74, 83, 90, 3, 1
];
// Step 1: Build frequency map
const freq = buildFrequencyMap(data);
// Step 2: Collect values that appear exactly once
const uniqueValues = collectGloballyUniqueValues(data, freq);
// Step 3: Choose how many unique random values to select
const N = 5;
// Step 4: Select N random unique values
const randomSelection = selectRandomUnique(uniqueValues, N);
// Step 5: Print results
console.log("Values that appear exactly once:");
printList(uniqueValues);
console.log("\nRandom selection (" + N + " values):");
printList(randomSelection);
})();
/*
run:
Values that appear exactly once:
12 33 59 61 17 74 83 90 1
Random selection (5 values):
12 90 33 1 17
*/
