Combinations in JS

combinations.js

// return all combinations of array elements for size n
// ex) combinations([1,2,3], 2) => [[1,2], [2,3], [1,3]]

// use backtracking & recursion
// iteration: for each element
// add element
// recurse with element
// remove element
// continue

function combinations(array, size) {
    let combos = [];

    function helper(chunk, n) {
        if (chunk.length == size) {
            combos.push(chunk.slice());
            return;
        }
        for(let i = n; i < array.length; i++) {
            chunk.push(array[i]);
            helper(chunk, i+1);
            chunk.pop();
        }
    }
    helper([], 0);
    return combos;
}

let result = combinations([1,2,3,4], 3);
console.log(result);

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