LeetCode.463 Island Perimeter

xiakexiaohu

于 2017-11-05 11:43:30 发布

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本文介绍了一种计算二维网格中岛屿周长的方法。通过遍历网格，统计岛屿的数量及相邻的岛屿，进而计算出岛屿的总周长。示例中给出了具体的实现代码。

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题目：

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:

分析：

class Solution {
    public int islandPerimeter(int[][] grid) {
        //给定一个二维方格，其中用1表示岛，0表示水，岛与岛之间可能相连，求这些岛围成的周长。
        //思路：求出总的岛的个数*4，减去相邻边*2，因为相邻两条边一定没有水相接。
        //注意：考虑相邻边，只需要类似前面unique path中的机器人走法（只考虑向下和向右两个方向）
        int count=0;
        int adjacent=0;
        
        for(int i=0;i<grid.length;i++){
            for(int j=0;j<grid[0].length;j++){
                if(grid[i][j]==1){
                    count++;
                    //向下判断
                    if(i!=grid.length-1&&grid[i+1][j]==1){
                        adjacent++;
                    }
                    //向右判断
                    if(j!=grid[0].length-1&&grid[i][j+1]==1){
                        adjacent++;
                    }
                }
            }
        }
        return count*4-adjacent*2;
    }
}