Topcoder SRM 642 div2

This is my third time in attending topcoder

and I got 815 grad T_T.


I think my skill and score will be higher than now if I continuously attend and study

http://community.topcoder.com/stat?c=problem_statement&pm=13553&rd=16085&rm=324592&cr=23054155


explanation : first I tried to solve this problem Brute-force Search

It mean all posiible I would search

this is may take O(n) if str length is higer time.

but I tried if str.length is cardinal number ,  find only center and one before, one after

and if str.length . even number search 3point, half and before of half, after of half



ex ) cardinal number : 129298481 : 1292 + 98481,  12929 + 8481

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public class ForgetfulAddition { public int minNumber(String str){ int len= str.length() ; int start = len / 2; int minNumber = Integer.MAX_VALUE; if(len % 2 == 1){ // 홀수 int sum = Integer.parseInt(str.substring(0, start)) + Integer.parseInt(str.substring(start, len)); minNumber = Math.min(sum, minNumber); sum = Integer.parseInt(str.substring(0, start+1)) + Integer.parseInt(str.substring(start+1, len)); minNumber = Math.min(sum, minNumber); }else{ // 짝수 int sum = Integer.parseInt(str.substring(0, start)) + Integer.parseInt(str.substring(start, len)); minNumber = Math.min(sum, minNumber); if(len >2){ sum = Integer.parseInt(str.substring(0, start+1)) + Integer.parseInt(str.substring(start+1, len)); minNumber = Math.min(sum, minNumber); sum = Integer.parseInt(str.substring(0, start-1)) + Integer.parseInt(str.substring(start-1, len)); minNumber = Math.min(sum, minNumber); } } return minNumber; } }

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public class LightSwitchingPuzzle { public int minFlips(String str){ char[] array = str.toCharArray(); int count =0; for(int i=0; i<array.length; i++){ if(array[i] == 'Y'){ count++; for(int j=i+1; j<array.length+1; j = j+ (i +1)){ array[j-1] = toggle(array[j-1]); } } } return count; } public char toggle(char a){ if(a =='Y'){ return 'N'; }else{ return 'Y'; } } }