463. Island Perimeter

Posted 2020-10-19 icychen

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:

大概意思就是求一个岛的周长

思路如下，分四个边处理，例如左边的边只有在最左边或者左边没有岛的时候可以算成周长，其余同理

public int islandPerimeter(int[][] grid) {
        int result = 0;
        for(int i=0;i<grid.length;i++)
        {
            for(int j=0;j<grid[0].length;j++)
            {
                if(grid[i][j]==0)
                {
                    continue;
                }
                else
                {
                    if(j==0||grid[i][j-1]==0)
                    {
                        result++;
                    }
                    if(i==0||grid[i-1][j]==0)
                    {
                        result++;
                    }
                     if(j==grid[0].length-1||grid[i][j+1]==0)
                    {
                        result++;
                    }
                     if(i==grid.length-1||grid[i+1][j]==0)
                    {
                        result++;
                    }
                }
            }
        }
        return result;
    }