845

class Solution {
public:
    int longestMountain(vector<int>& arr) {
        int ans=0, i=1;

        while(i<arr.size()){
            // Sideward move.
            while(i<arr.size() && arr[i] == arr[i-1])
                i++;

            // Upward move.
            int up = 0;
            while(i<arr.size() && arr[i] > arr[i-1])
                up++,i++;

            // Downward move.
            int down = 0;
            while(i<arr.size() && arr[i] < arr[i-1])
                down++, i++;

            if(up && down) ans = max(ans, up+down+1);
        }
        return ans;
    }
};