2210. Count Hills and Valleys in an Array

發表於 | 分類於

problem

solution

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class Solution {
public:
    int countHillValley(vector<int>& nums) {
        int n = nums.size();
        int count = 0;
        for(int i=1;i<n-1;++i){
            if(nums[i] > nums[i-1] ){
                // hills
                while(i<n-1 && nums[i] == nums[i+1])i++;
                if(i<n-1 && nums[i]>nums[i+1]) count++;
            }
            else if(nums[i]<nums[i-1]){
                // valley
                while(i<n-1 && nums[i] == nums[i+1]) i++;
                if(i<n-1 && nums[i] < nums[i+1]) count++;
            }
        }
        return count;
    }
};

analysis

  • time complexity O(n)
  • space complexity O(1)