LeetCode in Kotlin

329. Longest Increasing Path in a Matrix

Hard

Given an m x n integers matrix, return the length of the longest increasing path in matrix.

From each cell, you can either move in four directions: left, right, up, or down. You may not move diagonally or move outside the boundary (i.e., wrap-around is not allowed).

Example 1:

Input: matrix = [[9,9,4],[6,6,8],[2,1,1]]

Output: 4

Explanation: The longest increasing path is [1, 2, 6, 9].

Example 2:

Input: matrix = [[3,4,5],[3,2,6],[2,2,1]]

Output: 4

Explanation: The longest increasing path is [3, 4, 5, 6]. Moving diagonally is not allowed.

Example 3:

Input: matrix = [[1]]

Output: 1

Constraints:

• m == matrix.length
• n == matrix[i].length
• 1 <= m, n <= 200
• 0 <= matrix[i][j] <= 231 - 1

Solution

class Solution {
    fun longestIncreasingPath(matrix: Array<IntArray>): Int {
        var maxIncreasingSequenceCount = 0
        val n = matrix.size - 1
        val m = matrix[0].size - 1
        val memory = Array(n + 1) { IntArray(m + 1) }
        for (i in matrix.indices) {
            for (j in matrix[i].indices) {
                maxIncreasingSequenceCount = Math.max(maxIncreasingSequenceCount, move(i, j, n, m, matrix, memory))
            }
        }
        return maxIncreasingSequenceCount
    }

    private fun move(row: Int, col: Int, n: Int, m: Int, matrix: Array<IntArray>, memory: Array<IntArray>): Int {
        if (memory[row][col] == 0) {
            var count = 1
            // move down
            if (row < n && matrix[row + 1][col] > matrix[row][col]) {
                count = Math.max(count, move(row + 1, col, n, m, matrix, memory) + 1)
            }
            // move right
            if (col < m && matrix[row][col + 1] > matrix[row][col]) {
                count = Math.max(count, move(row, col + 1, n, m, matrix, memory) + 1)
            }
            // move up
            if (row > 0 && matrix[row - 1][col] > matrix[row][col]) {
                count = Math.max(count, move(row - 1, col, n, m, matrix, memory) + 1)
            }
            // move left
            if (col > 0 && matrix[row][col - 1] > matrix[row][col]) {
                count = Math.max(count, move(row, col - 1, n, m, matrix, memory) + 1)
            }
            memory[row][col] = count
        }
        return memory[row][col]
    }
}

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