LeetCode 463 Island Perimeter 岛周长

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本文介绍了一个算法问题：如何计算一个二维网格中岛屿的周长。通过遍历网格并检查每个岛屿单元的相邻区域来确定其边界，从而计算出岛屿的总周长。

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
Explanation: The perimeter is the 16 yellow stripes in the image below:
这里写图片描述

题目描述

给定二维的方格，1表示岛0表示水，方格其余部分被水填充，并且只存在一个岛，求岛的周长。

题目解析

由题目可以看出求周长的关键是不要计算重复的部分，只需要判断是否出现连着两个方格为1的情况，包括上下左右。

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