Calculating the length of the longest contiguous subsequence

maxSubArray.cpp

#include <iostream>
#include <vector>
using std::max;

// Let A be an array of length N
// Let M(i) be the largest contiguous subsequence ending at index i
// M(0) = 1
// M(i) = max(M(i),M(j)+1) for j<i and A[j]<=A[i]

int maxSubArray(int A[], int N) {
    if (N==0)return 0;
    std::vector<int> M(N);
    int best = M[0] = 1;
    for (int i = 1; i < N; ++i) {
        if (A[i-1]<=A[i]) M[i]=max(M[i],M[i-1]+1);
        best = max(best,M[i]);
    }
    return best;
}

template<class T,std::size_t N>
constexpr std::size_t size(T(&)[N]){return N;}

int main() {
    int arr[] = {1,-2,3,9,10,39,-2,2,5};
    std::cout << maxSubArray(arr,size(arr));
}