add solution to course schedule problem (#84)

Author: verma-anushka

C++/Course Schedule.cpp

@@ -0,0 +1,55 @@
+//Problem Statement: Course Schedule
+
+// There are a total of numCourses courses you have to take, labeled from 0 to numCourses-1.
+
+// Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: [0,1]
+
+// Given the total number of courses and a list of prerequisite pairs, is it possible for you to finish all courses?
+
+// Solution:
+// approach used to solve the problem: detect cycle in directed graph
+// if a back edge exists in the graph, it implies that there is a cycle, thus it is not possible to finish all the courses
+
+class Solution {
+public:
+ 
+ // helper function
+ bool dfs(vector<vector<int>>& adjlist, vector<int>& visited, int i) {
+ 
+ // base condition
+ if(visited[i]==1) return false;
+ visited[i]=1; // mark as being visited
+ 
+ for(int a:adjlist[i]) {
+ if(!dfs(adjlist, visited, a)) // dfs(adjlist, visited, a) == false
+ return false; 
+ }
+ 
+ visited[i] = 2; // mark as visited
+ return true; 
+ }
+ 
+ 
+ bool canFinish(int numc, vector<vector<int>>& prereq) {
+
+ // numc: numCourses
+ // prereq: prerequisites
+ 
+ // create adjacency list
+ vector<vector<int>> adjlist(numc, vector<int>());
+ for(vector<int>& p:prereq)
+ adjlist[p[0]].push_back(p[1]);
+ 
+ vector<int> visited(numc, 0); 
+ // unvisited: 0
+ // being visited: 1
+ // completely visited: 2
+ for(int i=0; i<numc; i++) {
+ if(visited[i]==0 && !dfs(adjlist, visited, i))
+ return false;
+ }
+ 
+ return true;
+ }
+ 
+};

README.md

@@ -68,12 +68,12 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 
 # Bit Manipulation
 
-| # | Title | Solution | Time | Space | Difficulty | Tag | Tutorial |
-| ---- | --------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------- | ------ | ------ | ---------- | --- | --------- |
-| 0136 | [Single Number](https://leetcode.com/problems/single-number/) | [Java](./Java/single-number.java) <br> [Python](./Python/single-number.py) <br> [C++](./C++/Single-Number.cpp) | _O(n)_ | _O(1)_ | Easy | | Using XOR |
-| 260 | [Single Number III](https://leetcode.com/problems/single-number-iii/) | [Python](./Python/single-number-iii.py) | _O(n)_ | _O(1)_ | Medium | | |
-| 476 | [Number Complement](https://leetcode.com/problems/number-complement/) | [Java](./Java/number-complement.java) | _O(1)_ | _O(1)_ | Easy | |  [Tutorial](https://youtu.be/6bp5V-O3zts)  |
-| 520 | [Detect Capital Use](https://leetcode.com/problems/detect-capital/) | [Python](./Python/detect-capital.py) | _O(n)_ | _O(1)_ | Easy | | |
+| # | Title | Solution | Time | Space | Difficulty | Tag | Tutorial  |
+| ---- | --------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------- | ------ | ------ | ---------- | --- | ---------------------------------------- |
+| 0136 | [Single Number](https://leetcode.com/problems/single-number/) | [Java](./Java/single-number.java) <br> [Python](./Python/single-number.py) <br> [C++](./C++/Single-Number.cpp) | _O(n)_ | _O(1)_ | Easy | | Using XOR  |
+| 260 | [Single Number III](https://leetcode.com/problems/single-number-iii/) | [Python](./Python/single-number-iii.py) | _O(n)_ | _O(1)_ | Medium | |  |
+| 476 | [Number Complement](https://leetcode.com/problems/number-complement/) | [Java](./Java/number-complement.java) | _O(1)_ | _O(1)_ | Easy | | [Tutorial](https://youtu.be/6bp5V-O3zts) |
+| 520 | [Detect Capital Use](https://leetcode.com/problems/detect-capital/) | [Python](./Python/detect-capital.py) | _O(n)_ | _O(1)_ | Easy | |  |
 
 <br/>
 <div align="right">
@@ -254,7 +254,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | ---- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------- | ------------------------- | ----------------- | ---------- | --- | ---- |
 | 1284 | [Minimum Number of Flips to Convert Binary Matrix to Zero Matrix](https://leetcode.com/problems/minimum-number-of-flips-to-convert-binary-matrix-to-zero-matrix/) | [C++](./C++/Minimum-Number-of-Flips-to-Convert-Binary-Matrix-to-Zero-Matrix.cpp) | _O(m * n * 2 ^ (m \* n))_ | _O(2 ^ (m \* n))_ | Hard | BFS | |
 | 200 | [Number of Islands](https://leetcode.com/problems/number-of-islands/) | [Java](./Java/NumberOfIslands.java) | O(R \* C) | O(R \* C) | Medium | BFS |
-| 200 | [Word Ladder](https://leetcode.com/problems/word-ladder/) | [Java](./Java/word-ladder.java) | O(N^2 \* M)  | O(N \* M) | Medium | BFS |
+| 200 | [Word Ladder](https://leetcode.com/problems/word-ladder/)  | [Java](./Java/word-ladder.java)  | O(N^2 \* M) | O(N \* M) | Medium | BFS |
 
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 <div align="right">
@@ -327,9 +327,10 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 
 # Graph
 
-| # | Title | Solution | Time | Space | Difficulty | Tag | Note |
-| ---- | --------------------------------------------------------------------------------------------------- | ------------------------------------------------------- | -------- | --------- | ---------- | ----- | -------------- |
-| 1042 | [Flower Planting with No Adjacent](https://leetcode.com/problems/flower-planting-with-no-adjacent/) | [Python](./Python/1042_FlowerPlantingwithNoAdjacent.py) | _O(V+E)_ | _O(2V+E)_ | Medium | Graph | Graph Coloring |
+| # | Title | Solution | Time | Space | Difficulty | Tag | Note |
+| ---- | --------------------------------------------------------------------------------------------------- | ------------------------------------------------------- | -------- | --------- | ---------- | ----- | --------------------------------- |
+| 207 | [Course Schedule](https://leetcode.com/problems/course-schedule/) | [C++](./C++/Course Schedule.cpp) | _O(V+E)_ | _O(V+E)_ | Medium | Graph | Cycle Detection in Directed Graph |
+| 1042 | [Flower Planting with No Adjacent](https://leetcode.com/problems/flower-planting-with-no-adjacent/) | [Python](./Python/1042_FlowerPlantingwithNoAdjacent.py) | _O(V+E)_ | _O(2V+E)_ | Medium | Graph | Graph Coloring |
 
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 <div align="right">