|17|[Letter Combinations of a Phone Number][017]|String, Backtracking|

|19|[Remove Nth Node From End of List][019]|Linked List, Two Pointers|

|33|[Search in Rotated Sorted Array][033]|Arrays, Binary Search|

|43|[Multiply Strings][043]|Math, String|

|554|[Brick Wall][554]|Hash Table|

[017]:https://github.com/Blankj/awesome-java-leetcode/blob/master/note/017/README.md

[019]:https://github.com/Blankj/awesome-java-leetcode/blob/master/note/019/README.md

[033]:https://github.com/Blankj/awesome-java-leetcode/blob/master/note/033/README.md

[043]:https://github.com/Blankj/awesome-java-leetcode/blob/master/note/043/README.md

[554]:https://github.com/Blankj/awesome-java-leetcode/blob/master/note/554/README.md

[004]:https://github.com/Blankj/awesome-java-leetcode/blob/master/note/004/README.md

Given two non-negative integers`num1` and`num2` represented as strings, return the product of`num1` and`num2`.

**Note:**

1. The length of both`num1` and`num2` is < 110.

2. Both`num1` and`num2` contains only digits`0-9`.

3. Both`num1` and`num2` does not contain any leading zero.

4. You**must not use any built-in BigInteger library** or**convert the inputs to integer** directly.

**Tags:** Math, String

题意是让你计算两个非负字符串的乘积，我们模拟小学数学的方式来做，一位一位模拟计算，再各位累加。

classSolution {

publicStringmultiply(Stringnum1,Stringnum2) {

if (num1.equals("0")|| num2.equals("0"))return"0";

int l1= num1.length(), l2= num2.length(), l= l1+ l2;

char[] ans=newchar[l];

char[] c1= num1.toCharArray();

char[] c2= num2.toCharArray();

for (int i= l1-1; i>=0;--i) {

int c= c1[i]-'0';

for (int j= l2-1; j>=0;--j) {

ans[i+ j+1]+= c* (c2[j]-'0');

}

}

for (int i= l-1; i>0;++i) {

if (ans[i]>9) {

ans[i-1]+= ans[i]/10;

ans[i]%=10;

}

}

StringBuilder sb=newStringBuilder();

int i=0;

for (; ;++i)if (ans[i]!=0)break;

for (; i< ans.length;++i) sb.append((char) (ans[i]+'0'));

return sb.toString();

}

}

如果你同我一样热爱数据结构、算法、LeetCode，可以关注我GitHub上的LeetCode题解：[awesome-java-leetcode][ajl]

[title]:https://leetcode.com/problems/multiply-strings

[ajl]:https://github.com/Blankj/awesome-java-leetcode

packagecom.blankj.medium._043;

publicclassSolution {

publicStringmultiply(Stringnum1,Stringnum2) {

if (num1.equals("0") ||num2.equals("0"))return"0";

intl1 =num1.length(),l2 =num2.length(),l =l1 +l2;

char[]ans =newchar[l];

char[]c1 =num1.toCharArray();

char[]c2 =num2.toCharArray();

for (inti =l1 -1;i >=0; --i) {

intc =c1[i] -'0';

for (intj =l2 -1;j >=0; --j) {

ans[i +j +1] +=c * (c2[j] -'0');

}

}

for (inti =l -1;i >0; --i) {

if (ans[i] >9) {

ans[i -1] +=ans[i] /10;

ans[i] %=10;

}

}

StringBuildersb =newStringBuilder();

inti =0;

for (; ; ++i)if (ans[i] !=0)break;

for (;i <ans.length; ++i)sb.append((char) (ans[i] +'0'));

returnsb.toString();

}

publicstaticvoidmain(String[]args) {

Solutionsolution =newSolution();

System.out.println(solution.multiply("132","19"));

}

}