SOURCE

var input = {"A":["B","C"],"B":["D","C","F"],"C":["E"],"D":[],"E":["D"],"F":["E","C"]};
		var arr = new Array();
		while(JSON.stringify(input) !="{}"){
			var res;
		    for(var key1 in input){
		        if(input[key1].length == 0){
		        	res = key1;
		        	console.log(res);
		        	delete input[key1];
		        	break;
		        }
		    }
		    for(var key2 in input){
		    	var a = input[key2];
		    	for(var k = 0; k < a.length; k++){
		    		if(a[k] == res){
		    			var del = a.splice(k,1);
		    		}
		    	}
		    }
		}
		console.log(arr);