拆数算法(ObjectiveC递归实现)

把一个大数拆成几个指定的小数相加，以下实现方式性能很差仅供参考：

- (NSMutableArray *)split:(NSInteger)number {
??? if (number < kThree) {
??????? return nil;
??? }
???
??? if ((number-kThree)==0 || (number-kFour)==0 || (number-kFive)==0) {
??????? NSMutableArray *_result = [NSMutableArray array];
???????
??????? NSMutableArray *_array = [NSMutableArray array];
??????? [_array addObject:[NSNumber numberWithInt:number]];
???????
??????? [_result addObject:_array];
??????? return _result;
??? }
???
??? NSInteger _left1 = number - kThree;
??? NSInteger _left2 = number - kFour;
??? NSInteger _left3 = number - kFive;
???
??? NSMutableArray *_total = [NSMutableArray array];
???
??? NSMutableArray *_rst1 = [self split:_left1];
??? if (!!_rst1 && (_rst1.count > 0)) {
??????? for (NSMutableArray *_a in _rst1) {
??????????? [_a addObject:[NSNumber numberWithInt:kThree]];
??????? }
??????? [_total addObjectsFromArray:_rst1];
??? }
???
??? NSMutableArray *_rst2 = [self split:_left2];
??? if (!!_rst2 && (_rst2.count > 0)) {
??????? for (NSMutableArray *_a in _rst2) {
??????????? [_a addObject:[NSNumber numberWithInt:kFour]];
??????? }
??????? [_total addObjectsFromArray:_rst2];
??? }
???
??? NSMutableArray *_rst3 = [self split:_left3];
??? if (!!_rst3 && (_rst3.count > 0)) {
??????? for (NSMutableArray *_a in _rst3) {
??????????? [_a addObject:[NSNumber numberWithInt:kFive]];
??????? }
??????? [_total addObjectsFromArray:_rst3];
??? }
???
??? return _total;
}