public int minDifficulty(int[] jobDifficulty, int d) {
        int N = jobDifficulty.length;
        if (N < d) return -1;

        int[][] dp = new int[d][N];
        dp[0][0] = jobDifficulty[0];
        for (int i = 1; i < N; ++i) {
            dp[0][i] = Math.max(dp[0][i-1], jobDifficulty[i]);
        }

        for (int k = 1; k < d; ++k) {
            for (int j = N-1; j >= k; --j){
                int max = Integer.MIN_VALUE;
                int min = Integer.MAX_VALUE;
                for (int i = j - 1; i >= k - 1; --i) {
                    max = Math.max(max, jobDifficulty[i+1]);
                    min = Math.min(min, dp[k - 1][i] + max);
                }
                dp[k][j] = min;
            }
        }

        return dp[d-1][N-1];
    }