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function summaryRanges(nums: number[]): string[] {    const ans = Array<string>();    let last = nums[0];    let start = nums[0];    for (const i of nums.keys()) {        const num = nums[i + 1];        if (num != last + 1) {            if (last === start) {                ans.push(String(last));            } else {                ans.push([start, last].join("->"));            }            start = num;        }        last = num;    }    return ans;}export default summaryRanges;