116 lines
4.4 KiB
C++
116 lines
4.4 KiB
C++
/*
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ID: philipp17
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PROG: beads
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LANG: C++
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*/
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/* LANG can be C++11 or C++14 for those more recent releases */
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#include <iostream>
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#include <fstream>
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#include <string>
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#include <algorithm>
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using namespace std;
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enum Colour{ red, blue, white };
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int main() {
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ofstream fout ("beads.out");
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ifstream fin ("beads.in");
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int n;
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string s;
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fin >> n >> s;
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string doubleNecklace = s.append(s);
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Colour lastBead = white, prewhiteBead = white;
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int currentLength = 0, redLength = 0, blueLength = 0, longestChain = 0, preWhiteLength = 0, inbetweenWhiteLength = 0;
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// The most intricate scenario is the following scenario:
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// white - red - white - blue - white
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// or equivalently:
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// white - blue - white - red - white
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// When white beads are enclosed by beads of the same colour we regard the beads as those colour
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for(const char& bead : doubleNecklace){
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if(bead == 'w'){
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if(lastBead == white){
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currentLength++;
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} else if(lastBead == red){
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prewhiteBead = red;
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redLength = currentLength;
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currentLength = 1;
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} else{ // Last bead is blue
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prewhiteBead = blue;
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blueLength = currentLength;
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currentLength = 1;
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}
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longestChain = max(longestChain, currentLength + redLength + blueLength + prewhiteBead + inbetweenWhiteLength);
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lastBead = white;
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} else if(bead == 'r'){
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if(lastBead == red){
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currentLength++;
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longestChain = max(longestChain, currentLength + preWhiteLength + blueLength + inbetweenWhiteLength);
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} else if(lastBead == blue){
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longestChain = max(longestChain, currentLength + redLength + preWhiteLength + inbetweenWhiteLength);
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blueLength = currentLength;
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redLength = 0;
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currentLength = 1;
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preWhiteLength = inbetweenWhiteLength;
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inbetweenWhiteLength = 0;
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} else{ // Last bead is white
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if(prewhiteBead == red){
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currentLength += redLength + 1;
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redLength = 0;
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longestChain = max(longestChain, currentLength + preWhiteLength + blueLength + inbetweenWhiteLength);
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} else{
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longestChain = max(longestChain, currentLength + blueLength + redLength + preWhiteLength + inbetweenWhiteLength);
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preWhiteLength = inbetweenWhiteLength;
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inbetweenWhiteLength = currentLength;
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redLength = 0;
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currentLength = 1;
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}
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}
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lastBead = red;
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} else if(bead == 'b'){
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if(lastBead == blue){
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currentLength++;
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longestChain = max(longestChain, currentLength + redLength + preWhiteLength + inbetweenWhiteLength);
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} else if(lastBead == red){
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longestChain = max(longestChain, currentLength + blueLength + preWhiteLength + inbetweenWhiteLength);
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redLength = currentLength;
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blueLength = 0;
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currentLength = 1;
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preWhiteLength = inbetweenWhiteLength;
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inbetweenWhiteLength = 0;
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} else{ // Last bead is white
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if(prewhiteBead == blue){
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currentLength += blueLength + 1;
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blueLength = 0;
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longestChain = max(longestChain, currentLength + redLength + preWhiteLength + inbetweenWhiteLength);
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} else{
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longestChain = max(longestChain, currentLength + blueLength + redLength + preWhiteLength + inbetweenWhiteLength);
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preWhiteLength = inbetweenWhiteLength;
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inbetweenWhiteLength = currentLength;
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blueLength = 0;
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currentLength = 1;
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}
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}
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lastBead = blue;
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} else{
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cout << "unexpected input" << endl;
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return 0;
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}
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// cout << bead << " CurrentLength: " << currentLength << " RedLength: " << redLength << " BlueLength: " << blueLength << " Prewhitelength: " << preWhiteLength << " Inbetweenwhite: " << inbetweenWhiteLength << " LongestChain: " << longestChain << endl;
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}
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fout << min(longestChain, int(s.size()) / 2) << endl;
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return 0;
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} |