leetcode 043 —— 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.

思路：纯粹分解乘法 ，按位加

class Solution {
public:
	string multiply(string num1, string num2) {
		if (num1 == "0" || num2 == "0") return "0";
		int m = num1.size();
		int n = num2.size();
		int *a = new int[m];
		int *b = new int[n];
		int *c = new int[m + n];
		memset(c, 0, (m+n)*sizeof(int));
	//	print(c, m + n);
		for (int i = 0; i < m; i++)
			a[i] = num1[i] - '0';
	//	print(a, m);
		for (int i = 0; i < n; i++)
			b[i] = num2[i] - '0';
	//	print(b, n);

		for (int i = 0; i < n; i++){
			for (int j = 0; j < m; j++){
				c[i + j+1] += b[i] * a[j];
			}
		}
//		print(c, m + n);
		int next = 0;
		int tmp = 0;
		for (int i = m + n - 1; i >= 0; i--){
			tmp = c[i] + next;
			next = tmp / 10;
			c[i] = tmp % 10;
		}
		string res;
		int i = 0;
		while (c[i] == 0) i++;
		for (i; i < m + n ; i++){
			res += char(c[i] + '0');
		}
		return res;
			
	}
};