add solution of problem 207: course schedule

Author: ppulse

CourseSchedule207/README.md

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+There are a total of *n* courses you have to take, labeled from `0` to `n - 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?
+
+For example:
+```
+2, [[1,0]]
+```
+There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible.
+```
+2, [[1,0],[0,1]]
+```
+There are a total of 2 courses to take. To take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible.
+
+#####Note:
+The input prerequisites is a graph represented by **a list of edges**, not adjacency matrices. Read more about how a graph is represented.

CourseSchedule207/Solution.java

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+public class Solution {
+    public boolean canFinish(int numCourses, int[][] prerequisites) {
+        if (prerequisites == null || prerequisites.length <= 1)
+            return true;
+            
+        for (int i = 0; i < prerequisites.length; i++) {
+            for (int j = 0; j < prerequisites.length; j++) {
+                if (prerequisites[i][1] == prerequisites[j][0]) {
+                    prerequisites[i][1] = prerequisites[j][1];
+                }
+                
+                if (prerequisites[i][0] == prerequisites[i][1])
+                    return false;
+            }
+        }
+        
+        return true;
+    }
+}