class Solution {
    public long countQuadruplets(int[] nums) {
        int n = nums.length;
        int[][] great = new int[n][n + 1];
        for(int k = n - 2; k >= 2; k -- ){
            great[k] = great[k + 1].clone();
            for(int x = 1; x < nums[k + 1]; x ++ ){
                great[k][x] ++ ;
            }
        }

        long ans = 0;
        int[] less = new int[n + 1];
        for(int j = 1; j < n - 2; j ++ ){
            for(int x = nums[j - 1] + 1; x <= n; x ++ ){
                less[x] ++ ;
            }
            for(int k = j + 1; k < n - 1; k ++ ){
                if(nums[j] > nums[k]){
                    ans += less[nums[k]] * great[k][nums[j]];
                }
            }
        }

        return ans;
    }
}