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Mileage #2 (Posted on 2024-05-11) Difficulty: 3 of 5
Refer to Mileage.

What pair of palindromic readings could they have so that it will take the most miles until they are both palindromes again? Is there any reading they could have so that they will NEVER both become palindromes?

No Solution Yet Submitted by K Sengupta    
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Solution No Subject | Comment 1 of 2
clearvars,clc
palTrip=double.empty(0);
palOdo=double.empty(0);
for i=0:99
  s=sprintf('%03d',10*i+floor(i/10));
  palTrip(i+1)=str2double(s);
end
trip=zeros(1,1000);
trip(palTrip+1)=1;
trip=repmat(trip,1,200);
for i=0:999
  s=sprintf('%03d',i);
  s=[s s(2) s(1)];
  palOdo(i+1)=str2double(s);
end
palOdo=[palOdo palOdo+100000];
odo=zeros(1,200000);
odo(palOdo+1)=1;

for offset=0:999
   hits=trip & odo;
   hits=find(hits);
   if length(hits)==0
     break
   end
   spans=hits(2:end)-hits(1:end-1);
   fmax=find(spans==max(spans));
   disp([offset max(spans) ])
   trip=[trip(2:end) trip(1)];
end

finds the maximum number between double palindromes for all 1000 offsets of the sequence of trip meters vs full odometers. All of them did find at least two double palindromes and reported the maximum distance apart. The largest of these maxima was 1910, indicating 1909 in a row that were not double maxima, with one double maximum a mile before that interval and one a mile after.

While any setting leads to at least two time seeing a pair of palindromes, there are four possible maximum distances between such pairs given some initial settings:

Depending on the phase relationship between the trip meter and the odometer, any of the below can be the longest distance from one double palindrome and the next:      
      
        1011
        1101
        1111
        1910
        
In each case the number of miles with no such pairing, between those with such a pairing, is 1 less than the distance between pairs.        
An example of the 1910 (with 1909 between) is:

 090 98089  double palinddrome
 091 98090
 092 98091
 093 98092
 094 98093
 095 98094
 096 98095
 097 98096
 098 98097
 099 98098
 100 98099
 101 98100
 102 98101
 103 98102
 104 98103
 105 98104
 106 98105
 107 98106
 108 98107
 109 98108
 110 98109
 111 98110
 112 98111
 113 98112
 114 98113
 115 98114
 116 98115
 117 98116
 118 98117
 119 98118
 120 98119
 121 98120
 122 98121
 123 98122
 124 98123
 125 98124
 126 98125
 127 98126
 128 98127
 129 98128
 130 98129
 131 98130
 132 98131
 133 98132
 134 98133
 135 98134

. . .

 960 99959
 961 99960
 962 99961
 963 99962
 964 99963
 965 99964
 966 99965
 967 99966
 968 99967
 969 99968
 970 99969
 971 99970
 972 99971
 973 99972
 974 99973
 975 99974
 976 99975
 977 99976
 978 99977
 979 99978
 980 99979
 981 99980
 982 99981
 983 99982
 984 99983
 985 99984
 986 99985
 987 99986
 988 99987
 989 99988
 990 99989
 991 99990
 992 99991
 993 99992
 994 99993
 995 99994
 996 99995
 997 99996
 998 99997
 999 99998
 000 99999  double palindrome



  Posted by Charlie on 2024-05-11 15:11:17
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