/*
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<number, number>.
2. Collect values that appear exactly once.
3. Shuffle the unique list using Fisher–Yates.
4. Take the first N values.
5. Return them and print them.
Notes:
- Uses modern TypeScript (ES6+).
- Uses expressive, structured functions.
*/
//---------------------------------------------------------------
// Build a frequency map: value -> count
//---------------------------------------------------------------
function buildFrequencyMap(data: number[]): Map<number, number> {
const freq: Map<number, number> = new Map<number, number>();
for (const value of data) {
const currentCount: number = freq.get(value) ?? 0;
freq.set(value, currentCount + 1);
}
return freq;
}
//---------------------------------------------------------------
// Collect values that appear exactly once
//---------------------------------------------------------------
function collectGloballyUniqueValues(
data: number[],
freq: Map<number, number>
): number[] {
const unique: number[] = [];
for (const value of data) {
const count: number | undefined = freq.get(value);
if (count === 1) {
unique.push(value);
}
}
return unique;
}
//---------------------------------------------------------------
// Randomly select N values from the unique list
//---------------------------------------------------------------
function selectRandomUnique(unique: number[], N: number): number[] {
let count: number = unique.length;
if (N > count) {
N = count; // clamp
}
// Shuffle using Fisher–Yates
const temp: number[] = [...unique];
for (let i: number = temp.length - 1; i > 0; i--) {
const j: number = Math.floor(Math.random() * (i + 1));
const swap: number = temp[i];
temp[i] = temp[j];
temp[j] = swap;
}
return temp.slice(0, N);
}
//---------------------------------------------------------------
// Print helper
//---------------------------------------------------------------
function printList(list: number[]): void {
console.log(list.join(" "));
}
//---------------------------------------------------------------
// Main program
//---------------------------------------------------------------
(function main(): void {
// Example array with duplicates
const data: number[] = [
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: Map<number, number> = buildFrequencyMap(data);
// Step 2: Collect values that appear exactly once
const uniqueValues: number[] = collectGloballyUniqueValues(data, freq);
// Step 3: Choose how many unique random values to select
const N: number = 5;
// Step 4: Select N random unique values
const randomSelection: number[] = 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 33 1 74 17
*/
