329.Longest Increasing Path in a Matrix

1-DFS + Memorization

https://leetcode.com/problems/longest-increasing-path-in-a-matrix/discuss/78308/

https://leetcode.com/problems/longest-increasing-path-in-a-matrix/solution/

class Solution {
    public int longestIncreasingPath(int[][] matrix) {
        if(matrix.length < 1)
            return 0;
        int m = matrix.length;
        int n = matrix[0].length;
        int[][] memo = new int[m][n]; // memory table;
        int[][] directions = {{-1, 0}, {1, 0}, {0, -1,}, {0, +1}};//four directions;
        int maxLength = 0;
        for(int i = 0; i < m; i++){
            for(int j = 0; j < n; j++){
                int currentLength = dfs(matrix, memo, directions, i, j);
                maxLength = Math.max(currentLength, maxLength);
            }
        }
        return maxLength;
    }

    public int dfs(int[][] matrix, int[][] memo, int[][] directions, int x, int y){
        if(memo[x][y] > 0)
            return memo[x][y];
        else{
            int maxLength = 1;
            for(int[] dir : directions){
                int newX = x + dir[0];
                int newY = y + dir[1];
                if(newX < 0 || newX >= matrix.length || newY < 0 || newY >= matrix[0].length || matrix[newX][newY] <= matrix[x][y])
                    continue;
                else{
                    int length = 1 + dfs(matrix, memo, directions, newX, newY);
                    maxLength = Math.max(length, maxLength);
                }
            }
            memo[x][y] = maxLength;
            return maxLength;
        }
    }
}