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public int solve (char[][] grid) {
        int ans = 0;
        int m = grid.length,n =grid[0].length;
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                if(grid[i][j]=='1'){
                    ans++;
                    dfs(grid, i, j);
                }
            }
        }
        return ans;
    }

    private void dfs(char[][] grid,int i,int j){
        if(i<0||j<0||i>=grid.length||j>=grid[0].length){
            return;
        }


        if(grid[i][j]=='0'){
            return;
        }

        grid[i][j]='0';
        dfs(grid, i-1, j);
        dfs(grid, i+1, j);
        dfs(grid, i, j-1);
        dfs(grid, i, j+1);
    }