假设,有一个数组为[1,2,3,4,5]；再给定一个数字如7，将数组间的值进行加法运算，怎么求出最后结果为[2,5]，[3,4]，[1,2,4]？</span>

 const sumArray = arr => arr.reduce((s, i) => s + i,0)
const newSpliceArray = (arr, index) => {
    let newArr = arr.slice(0)
    newArr.splice(index, 1)
    return newArr
}

const pickArrOfSum = function pickArrOfSum (arr = [], sum, base = [], set = new Set()) {
    const currentSum = sumArray(base)
    if (currentSum > sum) {
        // DO Nothing
    } else if (currentSum === sum) {
        set.add(base.sort().join(','))
    } else {
        arr.map((item, index) => {
            pickArrOfSum(newSpliceArray(arr, index), sum, base.concat(item), set)
        })
    }
    return set
}

// test
console.log(pickArrOfSum([1, 2, 3, 4, 5], 6))
console.log(pickArrOfSum([1, 2, 3, 4, 5], 7))
console.log(pickArrOfSum([1, 2, 3, 4, 5], 8))

复制到控制台运行即可看到结果