Summary Ranges

Problem

You are given a sorted unique integer array nums.

A range [a,b] is the set of all integers from a to b (inclusive).

Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is, each element of nums is covered by exactly one of the ranges, and there is no integer x such that x is in one of the ranges but not in nums.

Each range [a,b] in the list should be output as:

• "a->b" if a != b
• "a" if a == b

Constraints

• 0 <= nums.length <= 20
• -231 <= nums[i] <= 231 - 1
• All the values of nums are unique.
• nums is sorted in ascending order.

Solution

The problem Summary Ranges can be solved by repeating a process of recording a start index and expanding the range until a non-consecutive element is found.

Implementation

class Solution
{
  public:
    vector<string> summaryRanges(vector<int> &nums)
    {
        vector<string> ret;
        for (int i = 0; i < nums.size(); i++)
        {
            int idx = i;
            while (i < nums.size() - 1 && nums[i + 1] == nums[i] + 1)
                i++;

            if (nums[idx] == nums[i])
                ret.push_back(to_string(nums[idx]));
            else
                ret.push_back(to_string(nums[idx]) + "->" + to_string(nums[i]));
        }
        return ret;
    }
};