Add graph2 example

.gitignore

@@ -1,3 +1,3 @@
 /target
 .*
-cargo.lock
+Cargo.lock

examples/graph2.rs

@@ -0,0 +1,51 @@
+use metis::Graph;
+
+fn main() -> Result<(), metis::Error> {
+    // 5 - 3 - 4 - 0
+    //     |   | /
+    //     2 - 1
+    let adjncy = [1, 4, 0, 2, 4, 1, 3, 2, 4, 5, 0, 1, 3, 3];
+    let xadj = [0, 2, 5, 7, 10, 13, 14];
+
+    // iterate over adjacent nodes
+    let mut it = xadj
+        .windows(2)
+        .map(|x| &adjncy[x[0] as usize..x[1] as usize]);
+
+    // node 0 is adjacent to nodes 1 and 4
+    assert_eq!(it.next().unwrap(), &[1, 4]);
+    // node 1 is adjacent to nodes 0, 2, and 4
+    assert_eq!(it.next().unwrap(), &[0, 2, 4]);
+    // node 2 is adjacent to nodes 1 and 3
+    assert_eq!(it.next().unwrap(), &[1, 3]);
+    // node 3 is adjacent to nodes 2, 4, and 5
+    assert_eq!(it.next().unwrap(), &[2, 4, 5]);
+    // node 4 is adjacent to nodes 0, 1, and 3
+    assert_eq!(it.next().unwrap(), &[0, 1, 3]);
+    // node 5 is adjacent to node 3
+    assert_eq!(it.next().unwrap(), &[3]);
+    assert!(it.next().is_none());
+
+    let mut partition = vec![0; xadj.len() - 1];
+    let n_parts = 2;
+    Graph::new(1, n_parts, &xadj, &adjncy)?.part_kway(&mut partition)?;
+
+    // group 0 consists out of node 0, 1 and 4
+    // group 1 consists out of node 2, 3 and 5
+    assert_eq!(&partition, &[0, 0, 1, 1, 0, 1]);
+
+    let group = |group| {
+        partition
+            .iter()
+            .enumerate()
+            .filter(|(_, b)| **b == group)
+            .map(|(a, _)| a)
+            .collect::<Vec<_>>()
+    };
+    // group 0 consists out of node 0, 1 and 4
+    assert_eq!(&group(0), &[0, 1, 4]);
+    // group 1 consists out of node 2, 3 and 5
+    assert_eq!(&group(1), &[2, 3, 5]);
+
+    Ok(())
+}