[LeetCode] 43. Multiply Strings

题意很简单，给两个string做乘法。无需考虑一些比如string中夹杂字母的case。这里有一个discussion把思路已经解释的非常明白了，我就不讲思路了，直接上代码。

https://leetcode.com/problems/multiply-strings/discuss/17605/Easiest-JAVA-Solution-with-Graph-Explanation

 1 /**
 2  * @param {string} num1
 3  * @param {string} num2
 4  * @return {string}
 5  */
 6 var multiply = function(num1, num2) {
 7     let m = num1.length;
 8     let n = num2.length;
 9     let pos = new Array(m + n).fill(0);
10 
11     for (let i = m - 1; i >= 0; i--) {
12         for (let j = n - 1; j >= 0; j--) {
13             let mul = (num1.charAt(i) - '0') * (num2.charAt(j) - '0');
14             let p1 = i + j;
15             let p2 = i + j + 1;
16             let sum = mul + pos[p2];
17             pos[p1] += Math.floor(sum / 10);
18             pos[p2] = sum % 10;
19         }
20     }
21     let res = '';
22     for (let p of pos) {
23         if (!(res.length === 0 && p === 0)) {
24             res += p;
25         }
26     }
27     return res.length === 0 ? '0' : res;
28 };