Powerful Integer

class Solution {
    public int powerfulInteger(int[][] interval, int k) {
        int max = 0;
        for (int i = 0; i < interval.length; i++) {
            if (interval[i][1] > max)
                max = interval[i][1];
        }

        int[] arr = new int[max + 2];
        for (int i = 0; i < interval.length; i++) {
            arr[interval[i][0]] += 1;
            arr[interval[i][1] + 1] -= 1;
        }

        for (int i = 1; i < max + 2; i++)
            arr[i] = arr[i - 1] + arr[i];

        for (int i = max + 1; i >= 0; i--) {
            if (arr[i] >= k)
                return i;
        }

        return -1;
    }
}