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163. 缺失的区间

English Version

题目描述

给定一个排序的整数数组 nums ，其中元素的范围在 闭区间 [lower, upper] 当中，返回不包含在数组中的缺失区间。

示例：

输入: nums = [0, 1, 3, 50, 75], lower = 0 和 upper = 99,
输出: ["2", "4->49", "51->74", "76->99"]

解法

方法一：模拟

按照题意模拟即可。

时间复杂度 $O(n)$，忽略答案的空间消耗，空间复杂度 $O(1)$。其中 $n$ 为数组 nums 的长度。

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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