class Solution {
public:
    bool validMountainArray(vector<int>& arr) {
        if (arr.size()<3)
            return false;
        int i = 1;
        while(i<arr.size() && arr[i]>arr[i-1])
            i++;
        if (i==1||i==arr.size())
            return false;
        while(i<arr.size() && arr[i]<arr[i-1])
            i++;
        if (i==arr.size())
            return true;
        return false;
    }
};