problems(rs): add “785. Is Graph Bipartite?”

Signed-off-by: Matej Focko <me@mfocko.xyz>

problems/is-graph-bipartite.rs

@@ -0,0 +1,75 @@
+use std::collections::VecDeque;
+
+struct Solution {}
+impl Solution {
+    fn color(graph: &Vec<Vec<i32>>, start: usize, colors: &mut Vec<i32>) -> bool {
+        let mut q: VecDeque<usize> = VecDeque::new();
+        q.push_back(start);
+
+        while let Some(u) = q.pop_front() {
+            let u_color = colors[u];
+
+            let next_color = (colors[u] + 1) % 2;
+            for v in &graph[u] {
+                let v = *v as usize;
+                match colors[v] {
+                    -1 => {
+                        colors[v] = next_color;
+                        q.push_back(v);
+                    }
+                    _ => {
+                        if colors[v] != next_color {
+                            return false;
+                        }
+                    }
+                }
+            }
+        }
+
+        true
+    }
+
+    pub fn is_bipartite(graph: Vec<Vec<i32>>) -> bool {
+        let mut colors = vec![-1; graph.len()];
+
+        for u in 0..graph.len() {
+            if colors[u] != -1 {
+                continue;
+            }
+
+            colors[u] = 0;
+            if !Solution::color(&graph, u, &mut colors) {
+                return false;
+            }
+        }
+
+        true
+    }
+}
+
+fn main() {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn example_1() {
+        assert!(!Solution::is_bipartite(vec![
+            vec![1, 2, 3],
+            vec![0, 2],
+            vec![0, 1, 3],
+            vec![0, 2]
+        ]));
+    }
+
+    #[test]
+    fn example_2() {
+        assert!(Solution::is_bipartite(vec![
+            vec![1, 3],
+            vec![0, 2],
+            vec![1, 3],
+            vec![0, 2]
+        ]));
+    }
+}