Leetcode463. Island Perimeter-优快云博客

本文介绍了一个简单的方法来计算二维网格中岛屿的周长。通过遍历每个单元格，检查其上方和左侧是否为陆地来调整周长计数。

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ou 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
这里写图片描述

题目的意思就是求这个多边形的边长，因为只有一个多边形，所以直接遍历1出现的时候左面和上面是不是1就好，是的话加2，不是加4。

public static int islandPerimeter(int[][] grid) {
        int m = grid.length;
        int n =grid[0].length;
        int res =0;
        for (int i=0;i<m;i++){
            for (int j=0;j<n;j++){
                if (grid[i][j]==1){
                    res+=4;
                    if (i>0&&grid[i-1][j]==1){
                        res-=2;
                    }
                    if (j>0&&grid[i][j-1]==1){
                        res-=2;
                    }
                }

            }
        }
        return res;
    }