[leetcode] 941. Valid Mountain Array : https://leetcode.com/problems/valid-mountain-array/

Valid Mountain Array.cc

class Solution {
public:
    int SAME = 0;
    int UP = 1;
    int DOWN = -1;
    
    int getStatus(int diff){
        if(diff == 0) return SAME;
        return diff > 0 ? UP : DOWN;
    }
    
    bool validMountainArray(vector<int>& A) {
        if(A.size() < 3 || A[0] > A[1]) return false;
        bool isUp = true;
        for(int i=1;i<A.size();i++){
            int status = getStatus(A[i] - A[i-1]);
            if(status == SAME) return false;
            else if(status == UP){
                if(!isUp) return false;    
            }else{ // DOWN
                if(isUp) isUp = false;
            }
        }
        return !isUp;
    }
};