LeetCode 463. Island Perimeter

题目

You are given a map in form of a two-dimensional integer grid where 1 represents land and 0 represents water.

Grid cells are connected horizontally/vertically (not diagonally). The grid is completely surrounded by water, and there is exactly one island (i.e., one or more connected land cells).

The island doesn’t have “lakes” (water inside that isn’t connected to the water around the island). One cell is a square with side length 1. The grid is rectangular, width and height don’t exceed 100. Determine the perimeter of the island.

Example:

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Input:
[[0,1,0,0],
[1,1,1,0],
[0,1,0,0],
[1,1,0,0]]

Output: 16

Explanation: The perimeter is the 16 yellow stripes in the image below:

https://leetcode.com/problems/island-perimeter/

思路

每个位置的周长是4,如果和另一个陆地相连,那么这两个陆地周长和减去2.
所以整个小岛的周长是4×陆地数-2×相交数。

代码

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class Solution(object):
def islandPerimeter(self, grid):
"""
:type grid: List[List[int]]
:rtype: int
"""
m, n = len(grid), len(grid[0])
count = 0
neighbor = 0
for i in range(m):
for j in range(n):
if grid[i][j] == 1:
count += 1
if i < m-1:
if grid[i+1][j] == 1:
neighbor += 1
if j < n-1:
if grid[i][j+1] == 1:
neighbor += 1
return 4*count - 2*neighbor