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The main idea is to use a 3D dynamic programming array dp[i][j][k] where i and j represent the current position on the grid, and k represents the number of moves remaining. The value at dp[i][j][k] represents the number of ways to move the ball out of bounds using at most k moves starting from (i, j).
Transitions are made by moving the ball in one of the four possible directions and decreasing the move count. If the ball goes out of bounds, increment the path count. The answer is the sum of paths from startRow, startColumn using maxMove moves.
Time Complexity: O(m * n * maxMove) as each grid cell and move combination is processed exactly once.
Space Complexity: O(m * n * maxMove) due to the storage of the DP array.
1import java.util.Arrays;
2
3class Solution {
4 public int findPaths(int m, int n, int maxMove, int
The Java solution leverages a 3D array to track numbers of paths using dynamic programming. It adjusts through all directions accordingly and accumulates paths going out of the grid. It returns the module of the large possible results at the border.
DFS with memoization is used to prevent recalculating results for already evaluated states by storing them in a map or dictionary. Each call is a recursive attempt to move in all directions from the current cell, decrementing the move count. Result of out-of-bounds attempts is stored so it can be reused, avoiding exponential time complexity.
This algorithm uses a function that considers the current position and remaining moves. For every call, explore in four possible directions and add to the path count if the ball gets out of bounds. Store already calculated counts in a dictionary for path optimization.
Time Complexity: O(m * n * maxMove) where each state is visited only once.
Space Complexity: O(m * n * maxMove) due to memoization storage.
using namespace std;
class Solution {
vector<vector<vector<int>>> memo;
int MOD = 1000000007;
int dfs(int m, int n, int maxMove, int row, int column) {
if (row < 0 || column < 0 || row >= m || column >= n) return 1;
if (maxMove == 0) return 0;
if (memo[row][column][maxMove] != -1) return memo[row][column][maxMove];
int result = 0;
vector<vector<int>> directions = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
for (auto& dir : directions) {
result = (result + dfs(m, n, maxMove - 1, row + dir[0], column + dir[1])) % MOD;
}
return memo[row][column][maxMove] = result;
}
public:
int findPaths(int m, int n, int maxMove, int startRow, int startColumn) {
memo = vector<vector<vector<int>>>(m, vector<vector<int>>(n, vector<int>(maxMove + 1, -1)));
return dfs(m, n, maxMove, startRow, startColumn);
}
};This C++ implementation uses memoization with recursive depth-first search. It evaluates each cell, updating and reusing cached results for maximum move conditions. Successful exits beyond the grid add to the result count directly.