leetcode 矩陣中的最長遞增路徑 python【動態規劃】
阿新 • • 發佈:2018-12-24
題目描述
**分析:**假設最長路徑終點的是[i][j],則其最長路徑值為nums1[i][j],則nums1[i][j]等於它上下左右四個數中,比它小的數中最長路徑值最大的那一個+1
因此,我們可以從矩陣的最小值出發,其最長路徑值為1,然後計算第二小的數的最長路徑值,以此類推
class Solution: def longestIncreasingPath(self, matrix): """ :type matrix: List[List[int]] :rtype: int """ a = len(matrix) dic = {} nums_max = 1 if a == 0: nums_max = 0 else: b = len(matrix[0]) for i in range(a): for j in range(b): dic[(i,j)] = matrix[i][j] v = dic.keys() nums1 = [[1 for i in range(b)] for j in range(a)] dic = sorted(dic.items(),key = lambda x:x[1]) for k in dic: i = k[0][0] j = k[0][1] if (i+1,j) in v and matrix[i+1][j]<matrix[i][j] and nums1[i][j]<nums1[i+1][j]+1: nums1[i][j] = nums1[i+1][j] + 1 if (i,j+1) in v and matrix[i][j+1]<matrix[i][j] and nums1[i][j]<nums1[i][j+1]+1: nums1[i][j] = nums1[i][j+1] +1 if (i-1,j) in v and matrix[i-1][j]<matrix[i][j] and nums1[i][j]<nums1[i-1][j]+1: nums1[i][j] = nums1[i-1][j] +1 if (i,j-1) in v and matrix[i][j-1]<matrix[i][j] and nums1[i][j]<nums1[i][j-1]+1: nums1[i][j] = nums1[i][j-1] + 1 nums_max = max(nums_max,nums1[i][j]) return nums_max