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#include "leetcode.h"
class Solution {
public:
int kInversePairs(int n, int k) {
vector<int> dp(k + 1, 0);
int mod = 1e9 + 7;
for (int i = 1; i <= n; i++) {
vector<int> tmp(k + 1, 0);
tmp[0] = 1;
for (int j = 1; j <= k; j++) {
long long val = (dp[j] + mod - ((j - i) >= 0 ? dp[j - i] : 0)) % mod;
tmp[j] = (tmp[j - 1] + val) % mod;
}
dp = tmp;
}
return (dp[k] + mod - (k > 0 ? dp[k - 1] : 0)) % mod;
}
};
int main() {
Solution obj;
cout << obj.kInversePairs(3, 0);
}
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