public?int?binarySearch(int?num){
????int?left?=?1;
????int?right?=?num;
????while(true){
????????if(left?==?right){
????????????return?left;
????????}

????????int?mid?=?left?+??(right?-?left)/2;
????????int?res?=?binarySearch(mid);
????????if(res?==?0){
????????????return?mid;
????????}
????????if(res?==?1){
????????????left?=?mid?+?1;
????????}else{
????????????right?=?mid;
????????}
????}
}