Summary Ranges

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228.Summary Ranges

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

Example 1:

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Input: nums = [0,1,2,4,5,7]
Output: ["0->2","4->5","7"]
Explanation: The ranges are:
[0,2] --> "0->2"
[4,5] --> "4->5"
[7,7] --> "7"

Example 2:

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Input: nums = [0,2,3,4,6,8,9]
Output: ["0","2->4","6","8->9"]
Explanation: The ranges are:
[0,0] --> "0"
[2,4] --> "2->4"
[6,6] --> "6"
[8,9] --> "8->9"

时间复杂度：O(n)

空间复杂度：O(1)

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class Solution {
public:
    vector<string> summaryRanges(vector<int>& nums) {
        int nums_size = nums.size();
        if(nums_size == 0)return {};
        if(nums_size == 1)return {to_string(nums[0])};
        vector<string> ans_vec;
        for (int i = 0; i < nums_size-1; i++) {
            if (nums[i] != nums[i + 1] - 1)
                ans_vec.push_back(to_string(nums[i]));
            else {
                int temp = nums[i];
                while (i < nums_size - 1 && nums[i] == nums[i + 1] - 1)i++;
                ans_vec.push_back(to_string(temp) + "->" + to_string(nums[i]));
            }
        }
        if(nums[nums_size-1]!=nums[nums_size-2]+1)
            ans_vec.push_back(to_string(nums[nums_size-1]));
        return ans_vec;
    }
};

优化：

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class Solution {
public:
    vector<string> summaryRanges(vector<int>& nums) {
        vector<string> ret;
        int i = 0;
        int n = nums.size();
        while (i < n) {
            int low = i;
            i++;
            while (i < n && nums[i] == nums[i - 1] + 1) {
                i++;
            }
            int high = i - 1;
            string temp = to_string(nums[low]);
            if (low < high) {
                temp.append("->");
                temp.append(to_string(nums[high]));
            }
            ret.push_back(move(temp));
        }
        return ret;
    }
};