public class P0171ExcelSheetColumnNumber {

public int titleToNumber(String columnTitle){

int res=0;

int multi=1;

for(int i=columnTitle.length()-1;i>=0;i--){ //从后往前，看末位一共进了几次26；首次是26的0次方也就是1；

res=res+(columnTitle.charAt(i)-'A'+1)*multi;

multi*=26;

}

return res;

}

public int titleToNumber0(String columnTitle){

int res=0;

for (int i = 0; i < columnTitle.length(); ++i) {

res *= 26;//相当于向左边位移，类似于十进制中的左移进位

res += (columnTitle.charAt(i)-'A'+1);

}

return res;

}//从前往后，先进位（开始是0）再把末位加进去

}

/*

P0171ExcelSheetColumnNumber p171=new P0171ExcelSheetColumnNumber();

System.out.println(p171.titleToNumber("A"));

System.out.println(p171.titleToNumber("AB"));

System.out.println(p171.titleToNumber("ZY"));

System.out.println(p171.titleToNumber("FXSHRXW"));

*/