Improve performance by replacing bit_vec with fixedbitset.

Before:
    test bench_solve_100  ... bench:      53,365 ns/iter (+/- 651)
    test bench_solve_1000 ... bench:   5,864,809 ns/iter (+/- 102,059)
    test bench_solve_2000 ... bench:  34,347,333 ns/iter (+/- 200,639)

After:

    test bench_solve_100  ... bench:      41,574 ns/iter (+/- 765)
    test bench_solve_1000 ... bench:   4,693,452 ns/iter (+/- 189,201)
    test bench_solve_2000 ... bench:  29,954,973 ns/iter (+/- 438,573)

Cargo.toml

@@ -8,4 +8,4 @@ description = "Kuhn-Munkres (aka Hungarian) algorithm for solving the Assignment
 keywords = ["algorithm"]
 
 [dependencies]
-bit-vec = "*"
+fixedbitset = "0.1"

src/coverage.rs

@@ -1,10 +1,10 @@
-use bit_vec::BitVec;
+use fixedbitset::FixedBitSet;
 
 #[derive(Debug)]
 pub struct Coverage {
     n: usize,
-    rows: BitVec,
-    cols: BitVec,
+    rows: FixedBitSet,
+    cols: FixedBitSet,
 }
 
 impl Coverage {
@@ -13,19 +13,19 @@ impl Coverage {
     pub fn new(n: usize) -> Coverage {
         Coverage {
             n: n,
-            rows: BitVec::from_elem(n, false),
-            cols: BitVec::from_elem(n, false),
+            rows: FixedBitSet::with_capacity(n),
+            cols: FixedBitSet::with_capacity(n),
         }
     }
 
     #[inline]
     pub fn is_row_covered(&self, row: usize) -> bool {
-        self.rows[row]
+        self.rows.contains(row)
     }
 
     #[inline]
     pub fn is_col_covered(&self, col: usize) -> bool {
-        self.cols[col]
+        self.cols.contains(col)
     }
 
     #[inline]

src/lib.rs

@@ -17,7 +17,7 @@
 //    * More test cases
 //    * Non-square matrices
 
-extern crate bit_vec;
+extern crate fixedbitset;
 
 #[cfg(test)]
 extern crate test;