算法-键索引计数法

键索引计数法适合于整数分为较小的简单排序方法，基本的步骤分为四步:

1.统计每个分类出现的次数；

2.将分类的次数转换为对应的索引；

3.通过中间数组按照分类的权重对原始数组排序；

4.将排序之后中间数组赋值给原始数组；

基础定义

首先定义排序需要的需要类:

@interface keyIndexModel:NSObject

@property  (assign,nonatomic)  NSInteger  key;

@property  (strong,nonatomic)  NSString  *value;

-(instancetype)initWithKeyValue:(NSInteger)key  value:(NSString *)value;

@end

@interface KeyIndexSort : NSObject

-(void)sort:(NSMutableArray *)dataSource categoryNumber:(NSInteger)number;

@end

 　实现具体排序方法:

-(void)sort:(NSMutableArray *)dataSource categoryNumber:(NSInteger)number{
    NSInteger  len=[dataSource count];
    NSMutableArray  *tempArr=[[NSMutableArray alloc]initWithCapacity:1];
    //http://www.cnblogs.com/xiaofeixiang/
    for (NSInteger i=0; i<len; i++) {
        [tempArr addObject:[NSNull null]];
    }
    NSMutableArray *count=[[NSMutableArray alloc]initWithCapacity:1];
    for (NSInteger i=0; i<number+1; i++) {
        [count addObject:[NSNumber numberWithInteger:0]];
    }
    //统计每个分类的次数
    for (NSInteger i=0;i<len; i++) {
        keyIndexModel  *model=dataSource[i];
        count[model.key+1]=[NSNumber numberWithInteger:[count[model.key+1] integerValue]+1];
    }
    
    //将出现的次数转换为索引，第一组3次，第二组5次，因此对应第三组开始的索引是8
    for (NSInteger j=0; j<number; 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<len; m++) {
        keyIndexModel  *model=dataSource[m];
        tempArr[[count[model.key] integerValue]]=model;
        count[model.key]=[NSNumber numberWithInteger:[count[model.key] integerValue]+1];
    }
    //重新排序赋值
    for (NSInteger i=0; i<len; i++) {
        dataSource[i]=tempArr[i];
    }
    
}

排序测试

        NSMutableArray  *dataSource=[[NSMutableArray alloc]initWithCapacity:1];
        [dataSource addObject: [[keyIndexModel alloc]initWithKeyValue:0 value:@"FlyElephant"]];
        [dataSource addObject: [[keyIndexModel alloc]initWithKeyValue:1 value:@"keso"]];
        [dataSource addObject: [[keyIndexModel alloc]initWithKeyValue:2 value:@"中山郎"]];
        [dataSource addObject: [[keyIndexModel alloc]initWithKeyValue:3 value:@"http://www.cnblogs.com/xiaofeixiang/"]];
        [dataSource addObject: [[keyIndexModel alloc]initWithKeyValue:3 value:@"iOS技术交流:228407086"]];
        
        [dataSource addObject: [[keyIndexModel alloc]initWithKeyValue:2 value:@"北京"]];
        [dataSource addObject: [[keyIndexModel alloc]initWithKeyValue:1 value:@"上海"]];
        [dataSource addObject: [[keyIndexModel alloc]initWithKeyValue:3 value:@"深圳"]];
        [dataSource addObject: [[keyIndexModel alloc]initWithKeyValue:2 value:@"广州"]];
        [dataSource addObject: [[keyIndexModel alloc]initWithKeyValue:0 value:@"河南"]];
    
        KeyIndexSort  *indexSort=[[KeyIndexSort alloc]init];
        [indexSort sort:dataSource categoryNumber:5];
         [dataSource enumerateObjectsUsingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
             keyIndexModel  *model=obj;
             NSLog(@"%ld--%@",idx,model.value);
         }];

　排序结果: