Optimize range_query to match fenwick.c

Changes

1 changed files (+12/-2)

• src/fenwick.rs
  • @@ -32,8 +32,18 @@ ret
    } // Query for sum between indices i and j inclusive - pub fn range_query(f: &[i32], i: usize, j: usize) -> i32 { - query(f, j) - query(f, i - 1) + pub fn range_query(f: &[i32], mut i: usize, mut j: usize) -> i32 { + let mut ret = 0; + while j >= i { + ret += f[j]; + j -= j & j.wrapping_neg(); + } + i -= 1; + while i > j { + ret -= f[i]; + i -= i & i.wrapping_neg(); + } + ret } // Search for largest index with prefix sum less than or equal to s