计算--字符串相乘

LeetCode刷题记66

43. 字符串相乘

题目

class Solution {
    public String multiply(String num1, String num2) {
        List<List<Integer>> list = new ArrayList();
        int max = 0;
        for (int i = num1.length() - 1; i >= 0; i --) {
            List tmp = new ArrayList<Integer>();
            for (int j = 0; j < num1.length() - 1 - i; j ++) {
                tmp.add(0);
            }
            int f = 0;
            for (int j = num2.length() - 1; j >= 0; j--) {
                int n1 = num1.charAt(i) - '0';
                int n2 = num2.charAt(j) - '0';
                int num = n1 * n2 + f;
                f = num / 10;
                num %= 10;
                tmp.add(num);
            }
            if (f > 0) tmp.add(f);
            max = Math.max(max, tmp.size());
            list.add(tmp);
        }
        // System.out.println(num1.length());
        StringBuffer ans = new StringBuffer();
        int f = 0;
        for (int i = 0; i < max; i ++) {
            int sum = f;
            for (int j = 0; j < list.size(); j ++) {
                List<Integer> tmp = list.get(j);
                if (tmp.size() > i) sum += tmp.get(i);
            }
            f = sum / 10;
            sum = sum % 10;
            ans.append(sum + "");
        }
        if (f > 0) ans.append(f + "");
        int i = ans.length() - 1;
        for (;i >= 0; i --) {
            if (ans.charAt(i) != '0') {
                break; 
            }
        }
        if (i == -1) return "0";
        ans.delete(i + 1, ans.length());
        return ans.reverse().toString();
    }
}

3/5
66/150

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