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163. Missing Ranges

中文文档

Description

You are given an inclusive range [lower, upper] and a sorted unique integer array nums, where all elements are in the inclusive range.

A number x is considered missing if x is in the range [lower, upper] and x is not in nums.

Return the smallest sorted list of ranges that cover every missing number exactly. That is, no element of nums is in any of the ranges, and each missing number is in one of the ranges.

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

  • "a->b" if a != b
  • "a" if a == b

 

Example 1:

Input: nums = [0,1,3,50,75], lower = 0, upper = 99
Output: ["2","4->49","51->74","76->99"]
Explanation: The ranges are:
[2,2] --> "2"
[4,49] --> "4->49"
[51,74] --> "51->74"
[76,99] --> "76->99"

Example 2:

Input: nums = [-1], lower = -1, upper = -1
Output: []
Explanation: There are no missing ranges since there are no missing numbers.

 

Constraints:

  • -109 <= lower <= upper <= 109
  • 0 <= nums.length <= 100
  • lower <= nums[i] <= upper
  • All the values of nums are unique.

Solutions

Python3

class Solution:
    def findMissingRanges(self, nums: List[int], lower: int, upper: int) -> List[str]:
        def f(a, b):
            return str(a) if a == b else f'{a}->{b}'

        n = len(nums)
        if n == 0:
            return [f(lower, upper)]
        ans = []
        if nums[0] > lower:
            ans.append(f(lower, nums[0] - 1))
        for a, b in pairwise(nums):
            if b - a > 1:
                ans.append(f(a + 1, b - 1))
        if nums[-1] < upper:
            ans.append(f(nums[-1] + 1, upper))
        return ans

Java

class Solution {
    public List<String> findMissingRanges(int[] nums, int lower, int upper) {
        int n = nums.length;
        List<String> ans = new ArrayList<>();
        if (n == 0) {
            ans.add(f(lower, upper));
            return ans;
        }
        if (nums[0] > lower) {
            ans.add(f(lower, nums[0] - 1));
        }
        for (int i = 1; i < n; ++i) {
            int a = nums[i - 1], b = nums[i];
            if (b - a > 1) {
                ans.add(f(a + 1, b - 1));
            }
        }
        if (nums[n - 1] < upper) {
            ans.add(f(nums[n - 1] + 1, upper));
        }
        return ans;
    }

    private String f(int a, int b) {
        return a == b ? a + "" : a + "->" + b;
    }
}

C++

class Solution {
public:
    vector<string> findMissingRanges(vector<int>& nums, int lower, int upper) {
        auto f = [](int a, int b) {
            return a == b ? to_string(a) : to_string(a) + "->" + to_string(b);
        };
        int n = nums.size();
        vector<string> ans;
        if (n == 0) {
            ans.emplace_back(f(lower, upper));
            return ans;
        }
        if (nums[0] > lower) {
            ans.emplace_back(f(lower, nums[0] - 1));
        }
        for (int i = 1; i < n; ++i) {
            int a = nums[i - 1], b = nums[i];
            if (b - a > 1) {
                ans.emplace_back(f(a + 1, b - 1));
            }
        }
        if (nums[n - 1] < upper) {
            ans.emplace_back(f(nums[n - 1] + 1, upper));
        }
        return ans;
    }
};

Go

func findMissingRanges(nums []int, lower int, upper int) (ans []string) {
	f := func(a, b int) string {
		if a == b {
			return strconv.Itoa(a)
		}
		return strconv.Itoa(a) + "->" + strconv.Itoa(b)
	}
	n := len(nums)
	if n == 0 {
		ans = append(ans, f(lower, upper))
		return
	}
	if nums[0] > lower {
		ans = append(ans, f(lower, nums[0]-1))
	}
	for i := 1; i < n; i++ {
		a, b := nums[i-1], nums[i]
		if b-a > 1 {
			ans = append(ans, f(a+1, b-1))
		}
	}
	if nums[n-1] < upper {
		ans = append(ans, f(nums[n-1]+1, upper))
	}
	return
}

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