题目描述

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样例

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算法1

(二分查找左右端点) $O(logn)$

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时间复杂度

参考文献

C++ 代码

class Solution {
public:
    int getNumberOfK(vector<int>& nums, int k) {
        if (nums.empty()) return 0;

        int l = 0, r = nums.size() - 1;
        while (l < r){
            int mid = (l + r) >> 1;
            if (nums[mid] < k) l = mid + 1;
            else r = mid;
        }

        if (nums[l] != k) return 0;

        int left = l;

        l = 0, r = nums.size() - 1;
        while (l < r){
            int mid = (l + r + 1) >> 1;
            if (nums[mid] <= k) l = mid; 
            else r = mid - 1;
        }

        if (nums[r] != k) return 0;

        return r - left + 1;
    }
};

算法2

(暴力枚举) $O(n^2)$

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时间复杂度

参考文献

C++ 代码

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