From f83de5ee51c1985a5ee98a587416af142cbd1e2d Mon Sep 17 00:00:00 2001
From: Haidong Ji
Date: Thu, 16 Jul 2020 21:51:36 -0500
Subject: Graph BFS distance done.

---
 sources/bfs.py | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 sources/bfs.py

diff --git a/sources/bfs.py b/sources/bfs.py
new file mode 100644
index 0000000..5d28baa
--- /dev/null
+++ b/sources/bfs.py
@@ -0,0 +1,39 @@
+# Uses python3
+
+import sys
+import queue
+
+
+def bfs(adj, s, dist):
+    q = queue.Queue()
+    q.put(s)
+
+    while not q.empty():
+        u = q.get()
+        for i in adj[u]:
+            if dist[i] == -1:
+                q.put(i)
+                dist[i] = dist[u] + 1
+
+
+def distance(adj, s, t):
+    dist = [-1] * len(adj)
+    dist[s] = 0
+
+    bfs(adj, s, dist)
+
+    return dist[t]
+
+
+if __name__ == '__main__':
+    input = sys.stdin.read()
+    data = list(map(int, input.split()))
+    n, m = data[0:2]
+    data = data[2:]
+    edges = list(zip(data[0:(2 * m):2], data[1:(2 * m):2]))
+    adj = [[] for _ in range(n)]
+    for (a, b) in edges:
+        adj[a - 1].append(b - 1)
+        adj[b - 1].append(a - 1)
+    s, t = data[2 * m] - 1, data[2 * m + 1] - 1
+    print(distance(adj, s, t))
-- 
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