@Override
        public int compareTo(Pair o) {
            if(this.a <= o.a){
                return -1;
            }else{
                return 1;
            }
        }
http://www.geeksforgeeks.org/dynamic-programming-set-20-maximum-length-chain-of-pairs/
src/com/interview/dynamic/MaximumLengthChainPair.java