Longest Increasing Path in a Matrix
给一个2d数组, 找出其中最长的递增路径. 用dp作为一个memo. 然后用longest去记录路径的最长值. 因为题目不要求返回路径, 所以直接返回值就可以.
public class Solution {
public int longestIncreasingPath(int[][] matrix) {
if(matrix == null || matrix.length == 0)
return 0;
int n = matrix.length;
int m = matrix[0].length;
int[][]dp = new int[n][m];
int longest = 1;
for(int i = 0 ; i < n; i++) {
for(int j = 0; j < m; j++) {
longest = Math.max(longest, dfs(matrix,i,j,dp));
}
}
return longest;
}
public int dfs(int[][]matrix, int i , int j, int[][] dp) {
if(dp[i][j] > 0)
return dp[i][j];
int longest = 1;
int cur = matrix[i][j];
if(i-1>=0 && matrix[i-1][j] > cur) //up
longest = Math.max(longest, dfs(matrix, i-1,j,dp)+1);
if(i+1 <=matrix.length-1 && matrix[i+1][j] > cur) //down
longest = Math.max(longest, dfs(matrix, i+1,j,dp)+1);
if(j-1>=0 && matrix[i][j-1] > cur) //left
longest = Math.max(longest, dfs(matrix, i,j-1,dp)+1);
if(j+1 <=matrix[0].length-1 && matrix[i][j+1] > cur) // right
longest = Math.max(longest, dfs(matrix, i,j+1,dp)+1);
dp[i][j] = longest; //set memo
return dp[i][j];
}
}