Unique Paths III

class Solution {
public:
    int dfs(int i,int j,vector<vector<int>> grid,int zero){
        if(i<0 || j<0 || i>=grid.size() || j>=grid[0].size() || grid[i][j]==-1){
             return 0;
        }
        if(grid[i][j]==2){
           return zero==-1?1:0;
        }
        grid[i][j]=-1;
        zero--;
        int totalpaths=dfs(i+1,j,grid,zero)+dfs(i-1,j,grid,zero)+dfs(i,j+1,grid,zero)+dfs(i,j-1,grid,zero);
        grid[i][j]=0;
        zero++;
        return totalpaths;
    }
    int uniquePathsIII(vector<vector<int>>& grid) {
        int n=grid.size();
        int m=grid[0].size();
        int count=0;
        int sx=0;
        int sy=0;
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(grid[i][j]==0){
                    count++;
                }else if(grid[i][j]==1){
                   sx=i;
                   sy=j;
                }
            }
        }
        return dfs(sx,sy,grid,count);
    }
};