463. Island Perimeter

最新推荐文章于 2025-09-12 18:08:49 发布

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最新推荐文章于 2025-09-12 18:08:49 发布

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文章标签： java

原文链接：http://www.cnblogs.com/mengchunchen/p/7753267.html

本文介绍了一种计算二维网格中岛屿周长的方法。该方法适用于仅包含一个由陆地单元格组成的岛屿的情况，且岛屿内部没有湖泊。通过遍历网格，记录每个陆地单元格，并考虑其相邻的陆地单元格来减少重复计数，最终得出岛屿周长。

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:

[[0,1,0,0],
 [1,1,1,0],
 [0,1,0,0],
 [1,1,0,0]]

Answer: 16


求岛的周长

C++（196ms）：

 1 class Solution {
 2 public:
 3     int islandPerimeter(vector<vector<int>>& grid) {
 4         int count = 0 ;
 5         int repeat = 0 ;
 6         for(int i = 0 ; i < grid.size() ; i++){
 7             for(int j = 0 ; j < grid[0].size() ; j++){
 8                 if (grid[i][j] == 1){
 9                     count++ ;
10                     if (i!=0 && grid[i-1][j] == 1)
11                         repeat++ ;
12                     if (j!=0 && grid[i][j-1] == 1)
13                         repeat++ ;
14                 }
15             }
16         }
17         return count*4-repeat*2 ;
18     }
19 };

java(153ms):

 1 class Solution {
 2     public int islandPerimeter(int[][] grid) {
 3         int res = 0 ;
 4         for (int i = 0 ; i  < grid.length ; i++){
 5             for (int j = 0 ; j < grid[0].length ; j++){
 6                 if (grid[i][j] == 1){
 7                     res += 4 ;
 8                     if (i!=0 && grid[i-1][j] == 1)
 9                         res -= 2 ;
10                     if (j!=0 && grid[i][j-1] == 1)
11                         res -= 2 ;
12                 }
13             }
14         }
15         return res ;
16     }
17 }