iOS得到字符串中出现最多的字符和个数

（1）遍历字符串，得到字符对应个数字典

NSString *testStr = @"ffcnasjjkasjknkjasdjfkjdsakhjgakjkasnjkfnsjknkjnaj";
    NSMutableDictionary *dic = [[NSMutableDictionary alloc]init];

for (int i = 0; i < testStr.length; i ++) {
        NSString *str = [testStr substringWithRange:NSMakeRange(i,1)];
        if ([dic objectForKey:str] == nil) {
            [dic setObject:@"1" forKey:str];
        }else {
            [dic setObject:[NSString stringWithFormat:@"%d", [[dic objectForKey:str] intValue]+1 ] forKey:str];
        }
    }

（2）遍历字典，分别得到 key 和 value 数组

NSMutableArray *array1 = [[NSMutableArray alloc]init]; //key
    NSMutableArray *array2 = [[NSMutableArray alloc]init]; //value
    for (NSString *str in [dic allKeys]) {
        [array1 addObject:str];
        [array2 addObject:[dic objectForKey:str]];
    }

（3）得到最大value，并根据array2的index得到其对应的key

int MaxValue=[[array2 objectAtIndex:0] intValue];
    int maxIndex = 0;
    for (int i=1; i< [array2 count]; i++) {
        if ([[array2 objectAtIndex:i] intValue] > MaxValue) {
            MaxValue =[[array2 objectAtIndex:i] intValue];
            maxIndex = i;
        }
    }
    NSString *key = [array1 objectAtIndex:maxIndex];
    NSString *value = [array2 objectAtIndex:maxIndex];
    DLog(@"\n数量最多的字符为%@,%@个。",key,value);