汇总区间
    双指针方案
    [1]左指针永远指向区间的左边
     [2]右指针用于遍历整个数组
    [3]注意整个边界条件的处理（边界或者不连续）
     [4]注意 i 的移动

    1. var summaryRanges = function (nums) {
    2.     let res = [];
    3.     let i = 0;
    4.     //从0开始
    5.     for (let j = 0; j < nums.length; j++) {
    6.         //边界或者不连续的时候
    7.         if (j + 1 === nums.length || nums[j] + 1 !== nums[j + 1]) {
    8.             if (i === j) {
    9.                 res.push(nums[i] + '');
    10.             } else if (i < j) {
    11.                 res.push(nums[i] + '->' + nums[j]);
    12.             }
    13.             //注意切换i
    14.             i = j + 1;
    15.         }
    16.     }
    17.     return res;
    18. }
    19. const nums = [0, 1, 2, 4, 5, 7];
    20. console.log(summaryRanges(nums));

    自我版本实现

    var summaryRanges = function (nums) {
    let res = [];
    //特殊情况
    if (nums.length === 0) return res;
    if (nums.length === 1) {
        res.push(String(nums[0]));
        return res;
    }
    let [left, right] = [nums[0], null];
    for (let i = 1; i < nums.length; i++) {
        if (nums[i] === nums[i - 1] + 1) {
            right = nums[i];
        } else {
            if (right) {
                let str = left + '->' + right;
                res.push(str);
            } else {
                res.push(left + '');
            }
            [left, right] = [nums[i], null];
        }
    }
    res.push(left + (right !== null ? '->' + right : ''));
    return res;
};