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Straight forward idea. Just like the way we multiply numbers. Don‘t forget considering the carry and be careful. e.g.
123*456,
what we usually do is:
123
* 456
-----------
738
615
+492
-----------
56088
thus, 123*456 = 56088.
In the same way, the algorithm is:
from end to start position, use a new array to store temproary digit.
A*B
(1)For each element B[i]
Compute tmp = B[i]*A
Add tmp to the previous result, note the start position. res = res"+"tmp
(2)Return result.
To be specific,
(1) char2int, int(char-‘0‘);
(2) int2char, char(int+‘0‘)
(3) Don‘t forget the carry in each add or multiply operation.
(4) Don‘t forget the carry after last operation. e.g. 82+33 = 115.
(5) Be careful with the string order and the number order.
public class Solution { public String multiply(String num1, String num2) { //用字符串模拟乘法，注意事项见上面分析。注意result的第0位是结果的个位 int len1=num1.length(); int len2=num2.length(); int[] result=new int[len1+len2]; int carry=0; int i=0; int j=0; for( i=0;i<len2;i++){ int n2=num2.charAt(len2-1-i)-‘0‘; carry=0; for(j=0;j<len1;j++){ result[i+j]+=n2*(num1.charAt(len1-1-j)-‘0‘)+carry; carry=result[i+j]/10; result[i+j]%=10; } result[i+j]=result[i+j]+carry; } i=len1+len2-1; while(i>0){ if(result[i]!=0) break; i--; } StringBuilder res=new StringBuilder(); int k=i; while(k>=0){ res.append((char)(result[k]+‘0‘));//res.append(result[k]+‘0‘);会得整数，比如result[k]为0时，添加的是48 k--; } return res.toString(); } }
[leedcode 43] Multiply Strings
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原文地址：http://www.cnblogs.com/qiaomu/p/4637615.html
