463. Island Perimeter - LeetCode

Question

463. Island Perimeter

Solution

题目大意:给出一个二维数组1表示陆地0表示海,求陆地的周长

思路:

重新构造一张地图grid2即一个二维数组,比原数组大一圈,即长宽都大2
一个点在原地图坐标是(i,j),那么在重新构造的坐标就是(i+1,j+1)
遍历原地图,如果一是陆地,就遍历这个点的周围是否是海,如果是海线周长就加1

Java实现:

public int islandPerimeter(int[][] grid) {
    int total = 0;
    int[][] grid2 = new int[grid.length+2][grid[0].length+2];
    for (int i=0; i<grid.length; i++) {
        for (int j=0; j<grid[0].length; j++) {
            if (grid[i][j] == 1) {
                grid2[i+1][j+1] = 1;
            }
        }
    }

    for (int i=0; i<grid.length; i++) {
        for (int j=0; j<grid[i].length; j++) {
            int x = i+1;
            int y = j+1;
            if (grid2[x][y] == 0) continue;
            // left
            total += grid2[x-1][y]==1?0:1;
            // right
            total += grid2[x+1][y]==1?0:1;
            // top
            total += grid2[x][y-1]==1?0:1;
            // bottom
            total += grid2[x][y+1]==1?0:1;
        }
    }
    return total;
}