From 18c47b311522f0421e6cd479ff174093df1516e7 Mon Sep 17 00:00:00 2001
From: Santo Cariotti <santo@dcariotti.me>
Date: Thu, 19 Jan 2023 17:41:29 +0100
Subject: add bellman ford

---
 Year_2/Algorithms/bellman-ford.cc | 167 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 167 insertions(+)
 create mode 100644 Year_2/Algorithms/bellman-ford.cc

(limited to 'Year_2')

diff --git a/Year_2/Algorithms/bellman-ford.cc b/Year_2/Algorithms/bellman-ford.cc
new file mode 100644
index 0000000..0942646
--- /dev/null
+++ b/Year_2/Algorithms/bellman-ford.cc
@@ -0,0 +1,167 @@
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <vector>
+#define INF 9999999
+
+using namespace std;
+
+template <class H>
+class Graph {
+public:
+    Graph<H>*
+    add_node(H u)
+    {
+        auto it = nodes_.find(u);
+
+        if (it == nodes_.end()) {
+            nodes_.insert({ u, vector<pair<H, int>>() });
+            size_++;
+        }
+
+        return this;
+    }
+
+    Graph<H>*
+    add_edge(H u, H v, int w)
+    {
+        auto i = nodes_.find(u);
+        auto j = nodes_.find(v);
+
+        if (i != nodes_.end() && j != nodes_.end()) {
+            nodes_[u].push_back({ v, w });
+            edges_.push_back({ u, v, w });
+        }
+
+        return this;
+    }
+
+    void
+    bellmanford(H s, H r, ostream& out)
+    {
+        map<H, int> dist;
+        map<H, pair<H, int>> p;
+
+        for (const auto& it : nodes_) {
+            dist.insert({ it.first, INF });
+        }
+
+        dist[s] = 0;
+
+        for (size_t i = 0; i < size_; ++i) {
+            for (const auto& e : edges_) {
+                auto u = get<0>(e);
+                auto v = get<1>(e);
+                auto w = get<2>(e);
+
+                if (dist[u] != INF && dist[u] + w < dist[v]) {
+                    dist[v] = dist[u] + w;
+                    p[v] = make_pair(u, dist[v]);
+                }
+            }
+        }
+
+        for (size_t i = 0; i < size_; ++i) {
+            for (const auto& e : edges_) {
+                auto u = get<0>(e);
+                auto v = get<1>(e);
+                auto w = get<2>(e);
+
+                if (dist[u] != INF && dist[u] + w < dist[v]) {
+                    out << "undef." << endl;
+                    return;
+                }
+            }
+        }
+
+        if (p.find(r) == p.end()) {
+            out << "inf." << endl;
+            return;
+        } else {
+            out << p[r].second << endl;
+        }
+    }
+
+private:
+    // `nodes_` is map which has the node as key and the edges as value.
+    // eg:
+    // nodes_[0] = [[1, 300]];
+    // there is an edge 0<->1 with 300 as weight
+    map<H, vector<pair<H, int>>> nodes_;
+
+    vector<tuple<H, H, int>> edges_;
+
+    size_t size_ { 0 };
+};
+
+int
+main(int argc, char** argv)
+{
+    int ts = (argc > 1) ? stoi(argv[1]) : 100;
+    int n, m;
+    string tp;
+    string ch;
+    ifstream fin("input.txt");
+    ofstream fout("output.txt");
+
+    for (int i = 0; i < ts; ++i) {
+        fin >> n >> m >> tp;
+
+        if (tp == "int") {
+            Graph<int>* g = new Graph<int>();
+            int k, n1, n2, s, r;
+            int w;
+
+            for (int j = 0; j < n; ++j) {
+                fin >> k;
+                g->add_node(k);
+            }
+
+            for (int j = 0; j < m; ++j) {
+                fin >> ch;
+                n1 = stoi(ch.substr(1, ch.length()));
+                fin >> n2;
+                fin >> ch;
+                w = stoi(ch.substr(0, ch.length() - 1));
+
+                g->add_edge(n1, n2, w);
+            }
+
+            fin >> s >> r;
+
+            g->bellmanford(s, r, fout);
+
+            delete g;
+        } else if (tp == "double") {
+            Graph<int>* g = new Graph<int>();
+            double k, n1, n2, s, r;
+            int w;
+
+            for (int j = 0; j < n; ++j) {
+                fin >> k;
+                g->add_node(k * 10);
+            }
+
+            for (int j = 0; j < m; ++j) {
+                fin >> ch;
+                n1 = stod(ch.substr(1, ch.length()));
+                fin >> n2;
+                fin >> ch;
+                w = stoi(ch.substr(0, ch.length() - 1));
+
+                g->add_edge(n1 * 10, n2 * 10, w);
+            }
+
+            fin >> s >> r;
+
+            g->bellmanford(s * 10, r * 10, fout);
+
+            delete g;
+        }
+    }
+
+    fin.close();
+    fout.close();
+
+    return 0;
+}
-- 
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