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Use these hints if you're stuck. Try solving on your own first.
Let <code>dp[i][j]</code> denote the number of arrays of length <code>i</code> with <code>j</code> inversions.
<code>dp[i][j] = dp[i - 1][j] + dp[i - 1][j - 1] + … + dp[i - 1][0]</code>.
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<code>dp[i][j] = 0</code> if for some <code>x</code>, <code>requirements[x][0] == i</code> and <code>requirements[x][1] != j</code>.