Question

463. Island Perimeter

Solution

題目大意:給出一個二維數組1表示陸地0表示海,求陸地的周長

思路:

重新構造一張地圖grid2即一個二維數組,比原數組大一圈,即長寬都大2
一個點在原地圖坐標是(i,j),那麽在重新構造的坐標就是(i+1,j+1)
遍歷原地圖,如果一是陸地,就遍歷這個點的周圍是否是海,如果是海線周長就加1

Java實現:

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;
}
 

463. Island Perimeter - LeetCode