From d4da45aaeb3799ca813819086c53790e6cb3527d Mon Sep 17 00:00:00 2001
From: Haidong Ji
Date: Thu, 16 Jul 2020 21:06:20 -0500
Subject: BFS distance done. Following pseudo code, not too bad.

---
 src/main/BFS.java | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 src/main/BFS.java

diff --git a/src/main/BFS.java b/src/main/BFS.java
new file mode 100644
index 0000000..d56c134
--- /dev/null
+++ b/src/main/BFS.java
@@ -0,0 +1,53 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.Scanner;
+
+public class BFS {
+    private static int distance(ArrayList<Integer>[] adj, int s, int t) {
+        int[] dist = new int[adj.length];
+        Arrays.fill(dist, -1);
+        dist[s] = 0;
+
+        bfs(adj, s, dist);
+
+        return dist[t];
+    }
+
+    private static void bfs(ArrayList<Integer>[] adj, int s, int[] dist) {
+        Queue<Integer> vertexQ = new LinkedList<>();
+        vertexQ.add(s);
+
+        while (!vertexQ.isEmpty()) {
+            int u = vertexQ.remove();
+            for (int i : adj[u]) {
+                if (dist[i] == -1) {
+                    vertexQ.add(i);
+                    dist[i] = dist[u] + 1;
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int n = scanner.nextInt();
+        int m = scanner.nextInt();
+        ArrayList<Integer>[] adj = (ArrayList<Integer>[]) new ArrayList[n];
+        for (int i = 0; i < n; i++) {
+            adj[i] = new ArrayList<Integer>();
+        }
+        for (int i = 0; i < m; i++) {
+            int x, y;
+            x = scanner.nextInt();
+            y = scanner.nextInt();
+            adj[x - 1].add(y - 1);
+            adj[y - 1].add(x - 1);
+        }
+        int x = scanner.nextInt() - 1;
+        int y = scanner.nextInt() - 1;
+        System.out.println(distance(adj, x, y));
+    }
+}
+
-- 
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