# Backtracking Solution JavaScript with explanation

• ``````var combine = function(n, k) {
const result = []

function findCombinations(subArr, start) {
// basecase. If our subArray is the length of k, we push a copy of the array into result
if(subArr.length === k) {
result.push(arr.slice())
}

// We need all the numbers from 1..n, so we must loop from 1..n to get all values
for(let i = start; i <= n; i++) {
// for each iteration, we push into subArray the starting value to build the array
subArr.push(i)

// immediately recurse increasing the starting value of i by 1. We need this to build the subArr
// from [] -> [1] -> [1, 2]. The next value of i will allow the next value to be pushed into the subArr
findCombinations(arr, i+1)

// We remove the last value we added to clean subArr for the next new starting number.
// If we built all the values with 1, [1,2], [1,3], [1,4], we now pop 1 off and
// begin the loop with 2. [2, 3], [2, 4]
subArr.pop()
}
}

// start subArray with an empty array that we will populate. The problem states we need numbers
// from 1..n, so we start counting at 1
findCombinations([], 1)
return result
};
``````

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