#629. K Inverse Pairs Array

https://leetcode.com/problems/k-inverse-pairs-array/?envType=daily-question&envId=2024-01-28

function kInversePairs(n, k) {
    const MOD = 10**9 + 7;
    const store = new Array(n + 1).fill(0).map(() => new Array(k + 1).fill(0));

    store[0][0] = 1;

    for (let i = 1; i <= n; i++) {
        store[i][0] = 1;
        for (let j = 1; j <= k; j++) {
            store[i][j] = (store[i - 1][j] + store[i][j - 1]) % MOD;
            if (j >= i) {
                store[i][j] = (store[i][j] - store[i - 1][j - i] + MOD) % MOD;
            }
        }
    }

    return store[n][k];
}