Multiply Strings

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Multiply Strings

Given two numbers represented as strings, return multiplication of the numbers as a string.

Note: The numbers can be arbitrarily large and are non-negative.

Math String

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(M) Add Two Numbers (E) Plus One (E) Add Binary

class Solution {public:    string multiply(string num1, string num2)     {        string addDeci(string a,string b);                   string str;//默认为空串 //存储最后结果   string strBit;//存储一位相乘的结果.   if (num2.size()>num1.size())   {   string tmp=num1;   num1=num2;   num2=tmp;   }   if (num2=="0")   {   return "0";   }   int lengthA=num1.size();   int lengthB=num2.size();  //小的   int carry =0; //进位标志   char bitSum;   int MultiplySum;//每一次乘数个位的乘   for(int j=0;j<lengthB;j++)//j个相加..1,10,100   {   strBit="";   for(int i=0;i<lengthA;i++)   //每一位和他相加..   {    MultiplySum=(num2[lengthB-j-1]-'0')*(num1[lengthA-i-1]-'0')+carry;   carry=MultiplySum/10;  if(carry>0) //有进位  {                     MultiplySum=MultiplySum%10; bitSum='0'+MultiplySum;                     strBit=bitSum+strBit;  //每一次一个右边最小加入进来..  }  else  {  bitSum='0'+MultiplySum;  strBit=bitSum+strBit;  }   }   if(carry>0)   {   MultiplySum=carry;   bitSum='0'+MultiplySum; //char型   strBit=bitSum+strBit;   }    carry=0;   //加一位，10,20，两个数相加..  for (int Cntdigit=0;Cntdigit<j;Cntdigit++)//看移动多少位  {  strBit=strBit+"0";  }   str=addDeci(strBit,str);   }   return str;     }};string addDeci(string a,string b){string str;//默认为空串if (b.size()>a.size()){string tmp=b;b=a;a=tmp;}int lengthA=a.size();int lengthB=b.size();//最后一位与最后一位相加..int i=lengthA-1;int j=lengthB-1;int carry=0;int bit_Sum=0;char bitCurrent;while (j>=0) //先加最低位{bit_Sum=(a[i]-'0'+b[j]-'0')+carry; //计算每一位增加的数字if (bit_Sum/10>=1)  //1+1//有进位，自己变为2的余数{//之间记录到a[i]里面carry=bit_Sum/10; //进位bitCurrent=('0'+bit_Sum%10);str=bitCurrent+str;}else{carry=0;bitCurrent=('0'+bit_Sum); //convert to charstr=bitCurrent+str;}i--;j--;}while (i>=0){bit_Sum=(a[i]-'0')+carry;if (bit_Sum/10>=1)  //1+1{//之间记录到a[i]里面carry=bit_Sum/10; //进位bitCurrent=('0'+bit_Sum%10);  //1+1=2,+1=3str=bitCurrent+str;}else{carry=0; //没有进位bitCurrent=('0'+bit_Sum);str=bitCurrent+str;}i--;}if (carry>0){bitCurrent=('0'+carry);str=bitCurrent+str;return str;}return str;}

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