算法-低位优先的字符串排序

低位优先的字符串排序相当于是对键索引计数方法的一个扩展，主要用于处理固定长度字符串，比如说手机号，固定电话，银行卡卡号，字符串的长度为N，从右向左开始进行每个键作为值开始遍历，实现比较简单:

-(void)lowSort:(NSMutableArray *)dataSource singleLength:(NSInteger)len
{
    NSInteger  sourceCount=[dataSource count];
    NSInteger R=256;
    NSMutableArray  *tempArr=[[NSMutableArray alloc]initWithCapacity:1];
    for (NSInteger i=0; i<sourceCount; i++) {
        [tempArr addObject:[NSNull null]];
    }
    for (NSInteger d=len-1; d>=0; d--) {
        NSMutableArray  *count=[[NSMutableArray alloc]initWithCapacity:1];
        for (NSInteger i=0; i<R+1; i++) {
            [count addObject:[NSNumber numberWithInteger:0]];
        }
        //统计频率
        for (NSInteger i=0; i<sourceCount; i++) {
            NSString  *str=[dataSource objectAtIndex:i];
            NSInteger  charValue=[str characterAtIndex:d]-48;
            count[charValue+1]=[NSNumber numberWithInteger:[count[charValue+1] integerValue]+1];
        }
        for (NSInteger j=0; j<R; j++) {
            count[j+1]=[NSNumber numberWithInteger:[count[j] integerValue]+[count[j+1] integerValue]];
        }
        //将元素从上到下分类
        for (NSInteger m=0; m<sourceCount; m++) {
            NSString  *str=[dataSource objectAtIndex:m];
            NSInteger  charValue=[str characterAtIndex:d]-48;
            tempArr[[count[charValue] integerValue]]=dataSource[m];
            count[charValue]=[NSNumber numberWithInteger:[count[charValue] integerValue]+1];
        }
        //重新排序赋值
        for (NSInteger i=0; i<sourceCount; i++) {
            dataSource[i]=tempArr[i];
        }
    }
}

　代码测试:

LSD  *lsd=[[LSD alloc]init];
NSMutableArray  *dataSource=[[NSMutableArray alloc]initWithObjects:@"12345",@"23456",@"78901",@"89764",@"12345",@"45678",@"89794",@"89754",@"64532",@"69784",nil];
[lsd lowSort:dataSource singleLength:7];
[dataSource enumerateObjectsUsingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
    NSLog(@"%@",obj);
}];
NSLog(@"技术交流群:%@",@"228407086");
NSLog(@"博客园-FlyElephant:http://www.cnblogs.com/xiaofeixiang");