2850. Minimum Moves to Spread Stones Over Grid

Problem Statement

You are given a 0-indexed 2D integer matrix grid of size 3 * 3, representing the number of stones in each cell. The grid contains exactly 9 stones, and there can be multiple stones in a single cell.

In one move, you can move a single stone from its current cell to any other cell if the two cells share a side.

Return the minimum number of moves required to place one stone in each cell.

Example 1:

Input: grid = [[1,1,0],[1,1,1],[1,2,1]]
Output: 3
Explanation: One possible sequence of moves to place one stone in each cell is: 
1- Move one stone from cell (2,1) to cell (2,2).
2- Move one stone from cell (2,2) to cell (1,2).
3- Move one stone from cell (1,2) to cell (0,2).
In total, it takes 3 moves to place one stone in each cell of the grid.
It can be shown that 3 is the minimum number of moves required to place one stone in each cell.

Example 2:

Input: grid = [[1,3,0],[1,0,0],[1,0,3]]
Output: 4
Explanation: One possible sequence of moves to place one stone in each cell is:
1- Move one stone from cell (0,1) to cell (0,2).
2- Move one stone from cell (0,1) to cell (1,1).
3- Move one stone from cell (2,2) to cell (1,2).
4- Move one stone from cell (2,2) to cell (2,1).
In total, it takes 4 moves to place one stone in each cell of the grid.
It can be shown that 4 is the minimum number of moves required to place one stone in each cell.

Constraints:

• grid.length == grid[i].length == 3

• 0 <= grid[i][j] <= 9

• Sum of grid is equal to 9.

Intuition

Here BFS wont work, as stone collection is dependent on other

So we use Recursion and try all ways

Links

https://leetcode.com/problems/minimum-moves-to-spread-stones-over-grid/description/

Video Links

https://www.youtube.com/watch?v=Ew3C223hd-E&ab_channel=AryanMittal

Approach 1:

C++

class Solution {
public:
    vector<vector<int>> xtra,zero;
    int ret;
    void solve(int i, int count){
        if(i>=zero.size()){
            ret = min(ret, count);
            return;
        }

        for(int k=0; k<xtra.size(); k++){
            if(xtra[k][2] ==0)  continue;
            xtra[k][2]--;
            solve(i+1, abs(xtra[k][0] - zero[i][0]) + abs(xtra[k][1]-zero[i][1]) + count);
            xtra[k][2]++;
        }
    }

    int minimumMoves(vector<vector<int>>& grid) {
        for(int i=0; i<3; i++){
            for(int j=0; j<3; j++){
                if(grid[i][j] == 0)
                    zero.push_back({i,j});
                else if(grid[i][j] > 1)
                    xtra.push_back({i,j,grid[i][j]-1});
            }
        }

        if(zero.size() == 0)    return 0;
        ret = INT_MAX;
        solve(0,0);

        return ret;
    }
};

Approach 2:

C++

Approach 3:

C++

Approach 4:

C++

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