From 124c9f51b5c39b188956f4dad7fedafdfd3bcefd Mon Sep 17 00:00:00 2001
From: Sergiu Ivanov <sivanov@colimite.fr>
Date: Sun, 31 Oct 2021 22:19:53 +0100
Subject: [PATCH] Add bellman-ford.

---
 graph.rkt | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/graph.rkt b/graph.rkt
index 231753a..9c96332 100644
--- a/graph.rkt
+++ b/graph.rkt
@@ -39,6 +39,8 @@
 
            min-st-kruskal max-st-kruskal min-st-prim max-st-prim
 
+           bellman-ford
+
            graphviz)
 
   ;; Wrap the opaque graph structure coming from the generic
@@ -194,6 +196,10 @@
   (define (max-st-prim g source)
     (g:max-st-prim (gg g) source))
 
+  ;; 6 Single-source Shortest Paths
+  (define (bellman-ford g source)
+    (g:bellman-ford (gg g) source))
+
   ;; 10 Graphviz
   (define (graphviz g #:output [output #f] #:colors [colors #f])
     (g:graphviz (gg g) #:output output #:colors colors)))
@@ -285,6 +291,10 @@
   [min-st-prim (-> Graph Any (Listof (List Any Any)))]
   [max-st-prim (-> Graph Any (Listof (List Any Any)))]
 
+  ;; Single-source Shortest Paths
+  [bellman-ford (-> Graph Any (Values (Mutable-HashTable Any Number)
+                                      (Mutable-HashTable Any Any)))]
+
   ;; 10 Graphviz
   [graphviz (->* (Graph)
                  (#:output Output-Port
@@ -408,6 +418,15 @@
     (check-equal? (max-st-prim g0 'e)
                   '((a c) (e a) (c d) (c b))))
 
+  (test-case "6 Single-source Shortest Paths"
+    (define g0 (weighted-graph/directed '((1 a b) (2 a c) (3 b d) (3 c d))))
+
+    (define-values (bf-dists bf-pred) (bellman-ford g0 'a))
+    (check-equal? (hash->ordered-list bf-dists)
+                  '((a . 0) (b . 1) (c . 2) (d . 4)))
+    (check-equal? (hash->ordered-list bf-pred)
+                  '((a . #f) (b . a) (c . a) (d . b))))
+
   (test-case "10 Graphviz"
     (define g (directed-graph '((a b) (b c))))
     (check-equal? (graphviz g)