From 37da3962d275a2a566799f0fe430239b0cc53a55 Mon Sep 17 00:00:00 2001
From: yiakwy <yiak.wy@gmail.com>
Date: Tue, 29 Nov 2016 03:31:56 +0800
Subject: [PATCH] New method (non recursive) for CourseSchedule

---
 .../non-recursive/course_schedule.cpp         | 149 ++++++++++++++++++
 .../cpp/courseSchedule/non-recursive/main.cpp |  30 ++++
 2 files changed, 179 insertions(+)
 create mode 100644 algorithms/cpp/courseSchedule/non-recursive/course_schedule.cpp
 create mode 100644 algorithms/cpp/courseSchedule/non-recursive/main.cpp

diff --git a/algorithms/cpp/courseSchedule/non-recursive/course_schedule.cpp b/algorithms/cpp/courseSchedule/non-recursive/course_schedule.cpp
new file mode 100644
index 0000000..b7decde
--- /dev/null
+++ b/algorithms/cpp/courseSchedule/non-recursive/course_schedule.cpp
@@ -0,0 +1,149 @@
+//
+//  course_schedule.cpp
+//  LeeteCodeOJ#207
+//
+//  Created by Wang Yi on 28/11/16.
+//  Copyright (c) 2016 Wang Yi. All rights reserved.
+//
+
+#include <stdio.h>
+
+#include <stack>
+#include <queue>
+#include <vector>
+#include <unordered_set>
+
+using std::stack;
+using std::queue;
+using std::vector;
+using std::unordered_set;
+using std::pair;
+
+typedef pair<int, int> Val;
+typedef vector<unordered_set<int>> Graph;
+
+#define FOR(s, e) \
+for (s = 0; s < e; s++) {
+#define END ;}
+    
+    typedef struct _node {
+        int val;
+        // int depth;
+        struct _node * parent;
+    } node;
+    
+    class Solution {
+    public:
+        bool canFinish(int numCourses, vector<pair<int, int>>& prerequisites) {
+            vector<int> outdepth(numCourses, 0);
+            unordered_set<int> vex;
+            if ((int) prerequisites.size() == 0)
+                return true;
+            vector<unordered_set<int>> graph = to_neighbor_repr(numCourses, prerequisites, outdepth);
+            
+            return dsf(numCourses, graph, outdepth);
+        }
+        
+        vector<unordered_set<int>> to_neighbor_repr(int numOfvex, vector<Val>& edges,
+                                                    vector<int>& outdepth) {
+            // std::cout << "building ... " << std::endl;
+            vector<unordered_set<int>> graph(numOfvex);
+            for (auto edge : edges) {
+                graph[edge.second].insert(edge.first); // second -> first
+                outdepth[edge.second]++;
+                // std::cout << edge.first << " <- " << edge.second << std::endl;
+            }
+            
+            return graph;
+            
+        }
+        
+        
+        bool dsf(int numOfvex, vector<unordered_set<int>>& graph, vector<int>& outdepth)
+        {
+            // preparation
+            stack<node> s;
+            vector<bool> visited(numOfvex, false);
+            vector<bool> onpath(numOfvex, false);
+            vector<int> starts;
+            
+            int i;
+            
+            unordered_set<int> children;
+            
+            
+            FOR(i, numOfvex)
+            if (outdepth[i] !=0 ) {
+                starts.push_back(i);
+            }
+            END
+            
+            if ((int)starts.size() == 0)
+                return false; // no vertex with indepth of 0 found, a circle found
+            
+            for (auto j: starts) {
+                // std::cout << "start from " << j << std::endl;
+                // do dsf search, if not visited
+                // when a circle in a path found, return false.
+                // else return true
+                if (visited[j])
+                    continue;
+                
+                node head;
+                head.val = j;
+                head.parent = NULL;
+                // head.depth = 1;
+                s.push(head);
+                
+                // non-recursive search
+                while (!s.empty()) {
+                    node* curr = &(s.top());
+                    
+                    if (visited[curr->val]) {
+                        // all children have been read
+                        s.pop();
+                        onpath[curr->val] = false;
+                        continue; // ignore ...
+                    }
+                    
+                    onpath[curr->val] = visited[curr->val]= true;
+                    children = graph[curr->val];
+                    
+                    if ((int)children.size() == 0) {
+                        s.pop();
+                        onpath[curr->val] = false;
+                        // std::cout << "==== reach the end ===="<<std::endl;
+                        continue;
+                    }
+                    
+                    // std::cout << curr->val << "'s children is: ";
+                    for (auto child: children) {
+                        // std::cout << child << " ";
+                        //if (onpath.find(child) == onpath.end())
+                        if (onpath[child]) {
+                            
+                            // std::cout << std::endl << "a circle found:" << std::endl;
+                            // std::cout << child << " <- ";
+                            // while (curr->parent != NULL) {
+                            //     std::cout << curr->val << " <- ";
+                            //     curr = curr->parent;
+                            // }
+                            // std::cout << curr->val << std::endl;
+                            
+                            return false; // a circle found, might print debug here
+                        }
+                        
+                        node nd;
+                        nd.val = child;
+                        // nd.depth = curr->depth+1;
+                        nd.parent = curr; // for debug purpose ...
+                        s.push(nd);
+                    }
+                    // std::cout << std::endl;
+                }
+                
+            } // end of for
+            return true;
+        }
+        
+    };
\ No newline at end of file
diff --git a/algorithms/cpp/courseSchedule/non-recursive/main.cpp b/algorithms/cpp/courseSchedule/non-recursive/main.cpp
new file mode 100644
index 0000000..f667c87
--- /dev/null
+++ b/algorithms/cpp/courseSchedule/non-recursive/main.cpp
@@ -0,0 +1,30 @@
+//
+//  main.cpp
+//  LeeteCodeOJ#207
+//
+//  Created by Wang Yi on 28/11/16.
+//  Copyright (c) 2016 Wang Yi. All rights reserved.
+//
+
+#include <iostream>
+#include <string>
+#include <sstream>
+
+#include "course_schedule.cpp"
+
+using std::make_pair;
+
+int main(int argc, const char * argv[]) {
+    // insert code here...
+    Solution sl;
+    int numCourses = 4;
+    vector<Val> prerequisites;
+    prerequisites.push_back(make_pair<int, int>(0,1));
+    prerequisites.push_back(make_pair<int, int>(3,1));
+    prerequisites.push_back(make_pair<int, int>(1,3));
+    prerequisites.push_back(make_pair<int, int>(3,2));
+
+    
+    std::cout << sl.canFinish(numCourses, prerequisites);
+    return 0;
+}