200. Number of Islands

https://leetcode.com/problems/number-of-islands/description/

class UnionFound {
public:
    vector<int> v;
    int cnt;
    UnionFound(int n) {
        v = vector<int>(n);
        for (int i = 0; i < n; i++)
            v[i] = i;
        cnt = n;
    }
    int findParent(int i) {
        if (v[i] == i)  return i;
        v[i] = findParent(v[i]);
        return v[i];
    }
    void Union(int p, int c) {
        int pp = findParent(p);
        int cp = findParent(c);
        if (pp != cp) {
            v[cp] = pp;
            cnt--;
        }
    }
};
class Solution {
public:
    int numIslands(vector<vector<char>>& grid) {
        int m = grid.size(); if (m == 0)    return 0;
        int n = grid[0].size();  if (n == 0)    return 0;
        UnionFound unionFound(m*n);
        int dirs[] = { -1, 0, 1, 0, -1 };
        
        int zeros = 0;
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == '0')  zeros++;
                else {
                    for (int d = 0; d < 4; d++) {
                        int x = i + dirs[d];
                        int y = j + dirs[d+1];
                        if (x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == '1') {
                            unionFound.Union(i*n+j, x*n+y);
                        }
                    }
                }
            }
        return unionFound.cnt - zeros;
    }
};