iOS字符串反转

- (void)reverse {

    NSString* str =@"abcdefghigklmnopqrst";

    int length = (int)str.length;

    NSMutableString *finalStr = [NSMutableStringstringWithCapacity:length];

    for (int i = length -1; i >= 0; i--) {

        unichar c = [strcharacterAtIndex:i];

        [finalStr appendString:[NSStringstringWithFormat:@"%c", c]];

    }

    NSLog(@"======%@",finalStr);

}