Editing Openai/693843f2-4e44-8005-8882-a17446caa5c4 (section)

===== While iterating j from left to right: =====
* decrement current element from rightCount (because now j is not on the right anymore)
'' compute: - countLeft = leftCount[2 '' nums[j]] - countRight = rightCount[2 * nums[j]]
'' add countLeft '' countRight to answer
* increment leftCount[nums[j]]

=== <syntaxhighlight lang="java">class Solution { ===
    public int countTriplets(int[] nums) {
        int n = nums.length;
        long MOD = 1_000_000_007;

        Map<Integer, Integer> left = new HashMap<>();
        Map<Integer, Integer> right = new HashMap<>();

        // Fill right map with frequencies
        for (int x : nums) {
            right.put(x, right.getOrDefault(x, 0) + 1);
        }

        long ans = 0;

        for (int j = 0; j < n; j++) {
            int val = nums[j];

            // Remove nums[j] from the right side since j is current center
            right.put(val, right.get(val) - 1);

            int target = val * 2;

            long countLeft = left.getOrDefault(target, 0);
            long countRight = right.getOrDefault(target, 0);

            ans = (ans + (countLeft * countRight) % MOD) % MOD;

            // Add nums[j] to left map
            left.put(val, left.getOrDefault(val, 0) + 1);
        }

        return (int) ans;
    }
}

</syntaxhighlight>