### Problem

This is also like before problem. Here we have to find all valid sequences out of given number of courses and prerequesites.

### Example

Given number of courses :: 2

Prerequesites :: [[0,1]]

Output :: [0,1]

Given number of courses :: 2

Prerequesites :: [[0,1][1,0]]

Output :: []

### JavaScript Code

function findOrder(numCourses, prerequisites) { if(prerequisites == null){ return; } var len = prerequisites.length; //if there is no prerequisites, return a sequence of courses if(len == 0){ var res = []; for(var m=0; m<numCourses; m++){ res[m]=m; } return res; } //records the number of prerequisites each course (0,...,numCourses-1) requires var pCounter = []; //initialize result var result = []; for(var m=0; m<numCourses; m++){ pCounter[m]=0; result[m]=0; } for(var i=0; i<len; i++){ pCounter[prerequisites[i][0]]++; } //stores courses that have no prerequisites var queue = []; for(var i=0; i<numCourses; i++){ if(pCounter[i]==0){ queue.push(i); } } var numNoPre = queue.length; var j=0; while(queue.length!=0){ var c = queue.shift(); result[j++]=c; for(var i=0; i<len; i++){ if(prerequisites[i][1]==c){ pCounter[prerequisites[i][0]]--; if(pCounter[prerequisites[i][0]]==0){ queue.push(prerequisites[i][0]); numNoPre++; } } } } //return result if(numNoPre==numCourses){ return result; }else{ return []; } } console.log(findOrder(2, [[1,0]]));

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