Different algorithms

max.h

int arrayMax(int * a, int n) {
    if (n == 1) {
        return a[0];
    }
    return max(arrayMax(a, n-1), a[n-1]);
}

int arrayMax(int * a, int i, int j) {
    if (i >= j) {
        return a[i]; //or a[j]
    }
    return max(arrayMax(a, i, (i+j)/2), arrayMax(a, (i+j)/2+1, j));
}

reverse.h

void arrayReverse(int * a, int n) {
    int end = n-1
    for (int i = 0; i <= n/2; i++) {
        int temp = a[i];
        a[i] = a[n-i-1]
        a[n-i-1] = temp
    }
}

void arrayReverse(int * a, int i, int j) {
    if (i < j) {
        swap(a[i], a[j]);
        arrayReverse(a, i+1, j-1);
    }
}

sum.h

int arraySum(int * a, int n, int i) {
    if (i == n-1) {
        return a[n-1];
    }
    return (a[i] + arraySum(a, n, i+1));
}

int arraySum(int * a, int i) {
    if (i == 0) {
        return a[0];
    }
    return (a[i] + arraySum(a, i-1));
}

int arraySum(int * a, int i, int j) {
    if (i ==j) {
        return a[i];
    }
    return (arraySum(a, i, (i+j)/2) + arraySum(a, (i+j)/2+1, j);
}