941. Valid Mountain Array

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problem

solution

只會有一個peak

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class Solution {
public:
    bool validMountainArray(vector<int>& arr) {
        int n =arr.size();
        if(n<3) return false;
        int l =0 , r = n-1;
        while(l<r && arr[l] < arr[l+1]) l++;
        while(l<r && arr[r-1] > arr[r]) r--;
        return (l!=0) && (r!=n-1) &&(l==r);
    }
};

analysis

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