一、按照要求返回数组下标

给定整数数组 [a,b,c,...], 和整数d，满足a+b=d时，返回a、b的数组下标。

每种输入只会对应一个答案。数组中同一个元素不能使用两遍。

示例：

输入 [1,5,6,9], 7

输出 [0,2]

输入 [3,4,5,9,2], 9

输出 [1,2]

请编写一个满足以上要求的函数。

function fn(arr, num) {
            for (let i = 0; i < arr.length; i++) {
                for (let j = i + 1; j < arr.length; j++) {
                    if (arr[i] + arr[j] === num) {
                        return [i, j]
                    }
                }
            }
        }
        const res = fn([1, 5, 6, 9], 7)
        console.log(res);

二、计算微信运动步数

已知小明2020-08-16至2020-09-15的微信运动步数数据如下：

// steps[].step 步数
// steps[].timestamp 时间戳
const steps = [
  { step: 1753, timestamp: 1597507200000 },
  { step: 1637, timestamp: 1597593600000 },
  { step: 6216, timestamp: 1597680000000 },
  { step: 6466, timestamp: 1597766400000 },
  { step: 12998, timestamp: 1597852800000 },
  { step: 7731, timestamp: 1597939200000 },
  { step: 7115, timestamp: 1598025600000 },
  { step: 3603, timestamp: 1598112000000 },
  { step: 1659, timestamp: 1598198400000 },
  { step: 3582, timestamp: 1598284800000 },
  { step: 6979, timestamp: 1598371200000 },
  { step: 4567, timestamp: 1598457600000 },
  { step: 7639, timestamp: 1598544000000 },
  { step: 9150, timestamp: 1598630400000 },
  { step: 8565, timestamp: 1598716800000 },
  { step: 6544, timestamp: 1598803200000 },
  { step: 6316, timestamp: 1598889600000 },
  { step: 15523, timestamp: 1598976000000 },
  { step: 8254, timestamp: 1599062400000 },
  { step: 13552, timestamp: 1599148800000 },
  { step: 6163, timestamp: 1599235200000 },
  { step: 6338, timestamp: 1599321600000 },
  { step: 8508, timestamp: 1599408000000 },
  { step: 4002, timestamp: 1599494400000 },
  { step: 7501, timestamp: 1599580800000 },
  { step: 5922, timestamp: 1599667200000 },
  { step: 9635, timestamp: 1599753600000 },
  { step: 7067, timestamp: 1599840000000 },
  { step: 3878, timestamp: 1599926400000 },
  { step: 4088, timestamp: 1600012800000 },
  { step: 773, timestamp: 1600099200000 } 
]

请编写一个函数，将其中某个时间段的步数进行小计，返回小计结果

示例：

输入：2020-09-01, 2020-09-07

返回：64654

        function fn(date1, date2) {
            const time = steps.filter(it => {
                return it.timestamp >= +new Date(date1) && it.timestamp <= +new Date(date2)
            })
            return time.reduce((sum, it) => sum + it.step, 0)
        }

        const time = fn('2020-09-01 00:00:00', '2020-09-07 23:59:59')
        console.log(time);