Rotten Oranges (Leetcode)

class Solution {
public:
    int orangesRotting(vector<vector<int>>& grid) {
        // Code here
        int n = grid.size();
        int m = grid[0].size();
        queue<pair<int, int>> Queue;
        int fresh = 0;
        for(int i = 0; i < n; i++) {
            for(int j = 0; j < m; j++) {
                if(grid[i][j] == 2)
                Queue.push({i, j});
                else if(grid[i][j] == 1)
                    fresh++;
            }
        }
        pair<int, int> Pair[4] = {{0, -1}, {0, 1}, {1, 0}, {-1, 0}};
        int ans = -1;
        while(!Queue.empty()) {
            int s = Queue.size();
            ans++;
            for(int i = 0; i < s; i++) {
                pair<int, int> temp = Queue.front();
                Queue.pop();
                int currX = temp.first;
                int currY = temp.second;
                for(int j = 0; j < 4; j++) {
                    int x = currX + Pair[j].first;
                    int y = currY + Pair[j].second;
                    if(x >= 0 && x < n && y >= 0 && y < m && grid[x][y] == 1) {
                        Queue.push({x, y});
                        grid[x][y] = 2;
                        fresh--;
                    }
                }
            }
        }
        if(fresh > 0) return -1;
        if(ans == -1) return 0;
        return ans;
    }
};