class Solution {
    public String multiply(String num1, String num2) {
        if(num1.equals("0")|| num2.equals("0")){
            return "0";
        }
        StringBuilder res = new StringBuilder();
        int len1 = num1.length();
        int len2 = num2.length();
        int maxlen = 0;
        for (int i = len1 - 1; i >= 0; i--) {
            int n1 = num1.charAt(i) - 48;
            int add = 0;
            StringBuilder temp = new StringBuilder();
            for (int j = len2 - 1; j >= 0; j--) {
                int n2 = num2.charAt(j) - 48;
                int mul = n1 * n2;
                if(j != 0){
                    temp.append((mul+ add) % 10);
                    add = (mul+ add) / 10;
                }else {
                    StringBuilder s = new StringBuilder();
                    s.append(add + mul);
                    temp.append(s.reverse());
                }
            }
            temp = temp.reverse();
            for (int j = 0; j < len1 - 1 - i; j++) {
                temp.append(0);
            }
            maxlen = res.length() > temp.length() ? res.length() : temp.length();
            int add_2 = 0;
            temp.reverse();
            StringBuilder sb = new StringBuilder();
            for (int j = 0; j < maxlen; j++) {
                int a = j >= temp.length() ? 0 : temp.charAt(j) - 48;
                int b = j >= res.length() ? 0 : res.charAt(j) - 48;
                if(j == maxlen - 1){
                    StringBuilder s = new StringBuilder();
                    s.append(a + b + add_2);
                    sb.append(s.reverse());
                    break;
                }
                sb.append((a + b + add_2) % 10);
                add_2 = (a + b + add_2)/10;
            }
            res = sb;
        }
        return res.reverse().toString();
    }
}

class Solution {
    public String removeStars(String s) {
        StringBuilder res = new StringBuilder();
        int count = 0;
        for (int i = s.length() - 1; i >= 0; i--) {
            if(count == 0 && s.charAt(i) != '*') res.append(s.charAt(i));
            else if(s.charAt(i) == '*') count++;
            else count--;
        }
        return res.reverse().toString();
    }
}

class Solution {
        public int equalPairs(int[][] grid) {
        int res = 0;
        HashMap<String,Integer> map = new HashMap<>();
        for (int[] ints : grid) {
            StringBuilder stringBuilder = new StringBuilder();
            for (int i = 0; i < grid.length; i++) {
                stringBuilder.append(ints[i]).append(".");
            }
            map.put(stringBuilder.toString(),map.getOrDefault(stringBuilder.toString(),0)+ 1);

        }
        for (int i = 0; i < grid.length; i++) {
            StringBuilder stringBuilder = new StringBuilder();
            for (int[] ints : grid) {
                stringBuilder.append(ints[i]).append(".");
            }
            res += map.getOrDefault(stringBuilder.toString(),0);
        }
        return res;
    }
}