Given an integer matrix, find the length of the longest increasing path.
From each cell, you can either move to four directions: left, right, up or down. You may NOT move diagonally or move outside of the boundary (i.e. wrap-around is not allowed).
Example 1:
nums = [
[9,9,4],
[6,6,8],
[2,1,1]
]
Return 4
The longest increasing path is [1, 2, 6, 9].
Example 2:
nums = [
[3,4,5],
[3,2,6],
[2,2,1]
]
Return 4
The longest increasing path is [3, 4, 5, 6]. Moving diagonally is not allowed.
Solution:
public class Solution {
int[][] dirs = new int[][]{{0,1},{0,-1},{1,0},{-1,0}};
public int longestIncreasingPath(int[][] matrix) {
int m = matrix.length;
if(m==0) return 0;
int n = matrix[0].length;
int[][] cache = new int[m][n];
int max = 0;
for(int i=0; i<m; i++){
for(int j=0; j<n; j++){
max = Math.max(max, helper(matrix, cache, i, j));
}
}
return max;
}
public int helper(int[][] matrix, int[][] cache, int i, int j){
if(cache[i][j]!=0) return cache[i][j];
cache[i][j] = 1;
int m = matrix.length;
int n = matrix[0].length;
for(int[] d : dirs){
int x = i + d[0];
int y = j + d[1];
if(x>=0 && x<m && y>=0 && y<n && matrix[i][j]<matrix[x][y]){
cache[i][j] = Math.max(cache[i][j], helper(matrix, cache, x, y)+1);
}
}
return cache[i][j];
}
}