Merge pull request #529 from AnshShrivastava/master

Implemented Gale Shapley Algorithm in cpp

Author: probot-auto-merge[bot]

Matching/GaleShapley/galeshapley.cpp

@@ -0,0 +1,93 @@
+// Algorithm to find stable matching of companies and students where companies and students both provide their preference list and all matchings are stable
+// Implementation of Gale-Shapley Algorithm
+#include<bits/stdc++.h>
+using namespace std;
+// Funtion to check if found match is stable or not
+bool check_pair(int student, int match, vector<int> stud_list, vector<int> com_list, unordered_map<int, int> &m) {
+    int current = m[match];
+    int index_cur;
+    int index_stud;
+    for (int i = 0; i < stud_list.size(); i++) {
+        if (com_list[i] == current) 
+            index_cur = i;
+        if (com_list[i] == student)
+            index_stud = i;
+    }
+    if (index_stud>index_cur)
+        return false;
+    else return true;
+}
+// Function to find appropriate match for a student
+int find_pair(int student, vector<int> stud_list, vector<vector<int>> com_list, unordered_map<int, int> &m) {
+    int i = 0;
+    while (i<stud_list.size()){
+        int match = stud_list[i];
+        if (m.find(match) == m.end()) {
+            return match;
+        } else {
+            if (check_pair(student, match, stud_list, com_list[match-1], m)) {
+               m[match] = student;
+               return match;
+            } else {
+                i++;
+            }
+        }
+    }
+}
+// Function to implement Gale-Shapley Algorithm
+vector<pair<int, int>> Matcher(vector<vector<int>> stud_list, vector<vector<int>> com_list) {
+    unordered_map<int, int> m;
+    vector<pair<int, int>> matches;
+    int i =0, j =0;
+    int match;
+    while(m.size()<stud_list.size()) {
+        match = find_pair(i+1, stud_list[i], com_list, m);
+        //cout <<  "debug " << i+1 << " " <<match << endl;
+        m[match] = i+1;
+        i = (i+1)%stud_list.size();
+    }
+    for (auto i = m.begin(); i != m.end(); i++) {
+        matches.push_back(make_pair(i->second, i->first));
+    }
+    return matches;
+}
+// Comparator Function
+bool comp(pair<int, int> i, pair<int, int> j) {
+    return (i.first<j.first);
+}
+int main() {
+    //initializing the preference list
+    vector<vector<int>> stud_list;
+    vector<vector<int>> com_list;
+    vector<int> temp;
+    int tem;
+    int no_stud, no_com;
+    cout << "Enter no. of students and companies\n";
+    cin >> no_stud >> no_com;
+    cout << "Enter preference list of students\n";
+    for (int i = 0; i< no_stud; i++) {
+        for(int j =0; j<no_com; j++) {
+            cin >> tem;
+            temp.push_back(tem);
+        }
+        stud_list.push_back(temp);
+        temp.clear();
+    }
+    cout << "Enter preference list of companies\n";
+    for (int i = 0; i< no_com; i++) {
+        for(int j =0; j<no_stud; j++) {
+            cin >> tem;
+            temp.push_back(tem);
+        }
+        com_list.push_back(temp);
+        temp.clear();
+    }
+    cout << "Placing students...\n";
+    vector<pair<int, int>> matches(no_stud, make_pair(0, 0));
+    matches = Matcher(stud_list, com_list);
+    sort(matches.begin(), matches.end(), comp);
+    // Printing the Matched students
+    for (auto i = matches.begin(); i != matches.end();i++) {
+        cout << "Student: " << i->first << " is placed in " << "Company: " <<i->second <<endl;
+    }
+}