Hey! We did the same solution! This is what i did in Java:

public static long arrayManipulation(int n, int[][] queries) { long[] array = new long[n];

    for(int[] query : queries) {
        array[query[0] - 1] += query[2];

        if(query[1] < n) {
            array[query[1]] += (query[2] * -1);
        }

    }

    long max = 0;
    long currentVal = 0;

    for(int i = 0; i < n; i++) {
        currentVal += array[i];
        if(currentVal > max) {
            max = currentVal;
        }
    }

    return max;
}

I spent 2 days to come up with this solution, tho :( I feel so slow, i hope i can improve... I will !