463. Island Perimeter

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本文介绍了一道LeetCode上的编程题目——计算岛屿周长的方法。通过遍历二维矩阵，判断每个陆地单元格四周相邻的水域或边界数量来计算总周长。此算法简单高效，易于理解。

题目描述【Leetcode】

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

这道题直接就是循环来求包含的边，需要考虑边界条件

class Solution {
public:
    int islandPerimeter(vector<vector<int>>& grid) {
        int sum = 0;
        int n = grid.size();
        if(n == 0) return 0;
        int m = grid[0].size();
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
               if(grid[i][j] == 0)continue;
               if( j+1 == m || grid[i][j+1] == 0) sum++;
               if(j == 0 || grid[i][j-1] == 0) sum++;
               if(i+1 == n || grid[i+1][j] == 0) sum++;
               if(i == 0 ||grid[i-1][j] == 0) sum++;
            }
        }
        return sum;
    }
};