华为面试题目大整数乘法java代码

华为面试题目大整数乘法java代码

package cn.sunline.test;

/**
* @author huangzhongj
*
*/
public class BigInt3 {
public static String multiply(String s1, String s2) {
int iLengthBefore = s1.length();
if (s1.length() % 2 != 0) {
s1 = "0" + s1;
s2 = "0" + s2;
}
if (s1.length() <= 4) {
int i1 = Integer.valueOf(s1);
int i2 = Integer.valueOf(s2);
return i1 * i2 + "";
}
String sOneLeft = s1.substring(0, s1.length() / 2);
String sOneRight = s1.substring(s1.length() / 2);
String sTwoLeft = s2.substring(0, s1.length() / 2);
String sTwoRight = s2.substring(s1.length() / 2);
char[] arrCharHalf = new char[s1.length() / 2];
char[] arrCharTotal = new char[s1.length()];
for (int i = 0; i < arrCharTotal.length; i++) {
if (i > arrCharHalf.length - 1) {
arrCharTotal[i] = '0';
} else {
arrCharTotal[i] = '0';
arrCharHalf[i] = '0';
}
}
String sRight = multiply(sOneRight, sTwoRight);
String sCenter1 = multiply(sOneLeft, sTwoRight) + String.valueOf(arrCharHalf);
String sCenter2 = multiply(sOneRight, sTwoLeft) + String.valueOf(arrCharHalf);
String sLeft = multiply(sOneLeft, sTwoLeft) + String.valueOf(arrCharTotal);
String[] arrString = { sRight, sCenter1, sCenter2, sLeft };
char[] cResult = new char[iLengthBefore * 2];
for (int i = 0; i < cResult.length; i++) {
cResult[i] = '0';
}
for (String s : arrString) {
for (int i = 0; i < s.length(); i++) {
calOneWei(cResult, cResult.length - 1 - i, s.charAt(s.length() - 1 - i));
}
}
return moveZeroChar(cResult);
}

public static void main(String[] args) {
String s1 = "1234567891011121314151617181920";
String s2 = "2019181716151413121110987654321";
System.out.println(multiply(s1, s2));
}

public static void calOneWei(char[] arr, int iPosition, char cSummand) {
if (cSummand != '0') {
arr[iPosition] += cSummand;
if (arr[iPosition] > 105) {
arr[iPosition] = (char) (arr[iPosition] - 96 - 10 + 48);
calOneWei(arr, iPosition - 1, '1');
} else {
arr[iPosition] = (char) (arr[iPosition] - 96 + 48);
}
}
}

public static String moveZeroChar(char[] arrChar) {
int i;
for (i = 0; i < arrChar.length; i++) {
if (arrChar[i] != '0') {
break;
}
}
if (arrChar[0] == '0') {
char[] arrCharNew = new char[arrChar.length - i];
for (int j = i; j < arrChar.length; j++) {
arrCharNew[j - i] = arrChar[j];
}
return String.valueOf(arrCharNew);
}
return String.valueOf(arrChar);
}

}