0329

Author: theforestvn88

0301-0400/0329_longest_increasing_path_in_a_matrix.rb

@@ -0,0 +1,30 @@
+# @param {Integer[][]} matrix
+# @return {Integer}
+def longest_increasing_path(matrix)
+    rows = matrix.size.freeze
+    cols = matrix[0].size.freeze
+    directions = [[1,0], [-1,0], [0,1], [0,-1]].freeze
+    memo = Array.new(rows) { Array.new(cols) }
+    dfs = lambda { |r, c|
+        return memo[r][c] if memo[r][c]
+        
+        max = 1
+        directions.each { |dr, dc|
+            next_r = r + dr
+            next_c = c + dc
+            if next_r >= 0 && next_c >= 0 && next_r < rows && next_c < cols && matrix[r][c] < matrix[next_r][next_c]
+                max = [max, 1 + dfs.call(next_r, next_c)].max
+            end
+        }
+        memo[r][c] = max
+    }
+
+    longest = 0
+    (0...rows).each { |r|
+        (0...cols).each { |c|
+            longest = [longest, dfs.call(r, c)].max
+        }
+    }
+
+    longest
+end