Q-10 Unique Paths II - LeetCode

class Solution {
    public int uniquePathsWithObstacles(int[][] grid) {
        int m = grid.length , n = grid[0].length;

        //if first cell is 1 only , first cell is not checked in recursion
        if(grid[m-1][n-1] == 1) 
        return 0;
        // return solve(grid , m-1 , n-1 , new Integer[m][n]);

        //tabulization -> 2*m*n | Sc - m*n (dp array)
        int[][] dp = new int[m][n];
        // dp[0][0] = 1;

        for(int i = 0 ;i < m ; i++){
            for(int j =0 ; j < n ; j++){
                
                //base case
                if(i == 0 && j == 0)
                dp[i][j] = 1;

                else{
                    int down = 0 , right = 0;
    
                    if(i-1 >= 0 && grid[i-1][j] != 1)
                    down = dp[i-1][j];

                    if(j-1>=0 && grid[i][j-1] != 1)
                    right = dp[i][j-1];
                    
                    dp[i][j] = (down + right);
                }
            }
        }
        return dp[m-1][n-1];
    }

    //recursion 2^(m*n) + memoization 2*m*n| Sc- m*n(recursion stack height) + m*n(dp array)
    public int solve(int[][] grid , int r , int c , Integer[][] dp ){
        
        if(r == 0 && c == 0 )
        return 1;    

        if(dp[r][c] != null)
        return dp[r][c];

        int down = 0 , right = 0;
        
        if(r-1 >= 0 && grid[r-1][c] != 1)
        down = solve(grid , r-1,c ,dp);

        if(c-1>=0 && grid[r][c-1] != 1)
        right = solve(grid , r , c-1 , dp);

        return dp[r][c] = (down + right);
    }
}