LeetCode 941. 有效的山脉数组

class Solution {
public:
    bool validMountainArray(vector<int>& A) {
        int N = A.size();
        int i = 0;

        // walk up
        while (i+1 < N && A[i] < A[i+1])
            i++;

        // peak can't be first or last
        if (i == 0 || i == N-1)
            return false;

        // walk down
        while (i+1 < N && A[i] > A[i+1])
            i++;

        return i == N-1;


    }
};

class Solution {
public:
    bool validMountainArray(vector<int>& A) {
        int a=0,b=A.size()-1;
        while(a+1<A.size()&&A[a+1]>A[a]){
            a++;
        }
        while(b>0&&A[b]<A[b-1]){
            b--;
        }
        cout<<a<<" "<<b;
        return a!=0&&a==b&&b!=A.size()-1;
    }
};