diff options
Diffstat (limited to 'content')
| -rw-r--r-- | content/math/divSum.cpp | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/content/math/divSum.cpp b/content/math/divSum.cpp new file mode 100644 index 0000000..dc4bc4d --- /dev/null +++ b/content/math/divSum.cpp @@ -0,0 +1,9 @@ +// Calculates the sum of (a*i+b)/m for i=0..(n-1) in O(log(n)) +// Note that b should not be negative! +ll divSum(ll n, ll m, ll a, ll b){ + if(m == 0) return 0; + ll ans = a/m * n*(n-1) / 2 + b/m * n; + a %= m, b %= m; + ll y = (a*(n-1)+b)/m; + return ans + y*(n-1) - divSum(y, a, m, m-b-1); +}
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