Leetcode Finding Maximum Area of Island Solution

Question

Given a non-empty 2D array grid of 0's and 1's, an island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water. (LeetCode)

This is my code

int maxAreaOfIsland(vector<vector<int>>& grid) { int max_area = 0; int rows = grid.size(); int columns = grid[0].size(); vector<vector<bool>> visited(rows, vector<bool>(columns,false)); for(int i=0 ; i < rows ; ++i){ for(int j=0; j < columns ; ++j){ max_area = max(max_area, area(i,j,grid,visited)); } } return max_area; } int area(int row, int col, vector<vector<int>>& grid, vector<vector<bool>>& visited){ if(row < 0 || row >= grid.size() || col < 0 || col >= grid[row].size() || visited[row][col]==true || grid[row][col] == 0) return 0; visited[row][col] = true; return (1 + area(row-1,col,grid,visited) + area(row,col-1,grid,visited) + area(row+1,col,grid,visited) + area(row,col+1,grid,visited)); } 

It was accepted on LeetCode and worked for all test cases. As you can see, the readability of the code is not good, so I am looking for a Code Review:

1. How can I improve readability in if() construct and return in area function?

2. Is there a better way to initialize 2D Vector in C++?

3. Is there a better way to maintain the visited array? I had to pass that array in every function call. If this data member is declared as as a static data member of the class then can its passing in every recursive call be avoided?