Island Perimeter

最新推荐文章于 2020-10-30 10:03:28 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。该方法适用于由1（陆地）和0（水域）组成的矩阵，其中岛屿定义为至少一个或多个相连的陆地单元，且不包含内部湖泊。通过遍历每个单元格并检查相邻单元格的状态来确定总周长。

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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:

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int islandPerimeter(int** grid, int gridRowSize, int gridColSize) {
    int res = 0;

    for(int i=0;i<gridRowSize;i++)
    for(int j=0;j<gridColSize;j++)
    if(grid[i][j]){
        res+=4;
        if(i&&grid[i-1][j])res-=2;
        if(j&&grid[i][j-1])res-=2;
    }
    return res;
}

int islandPerimeter(int** grid, int gridRowSize, int gridColSize) {
    int res = 0;

    for(int i=0;i<gridRowSize;i++)
    for(int j=0;j<gridColSize;j++)
    if(grid[i][j]){
        if(i==0)res+=1;else res+=(1^grid[i-1][j]);
        if(j==0)res+=1;else res+=(1^grid[i][j-1]);
        if(j==gridColSize-1)res+=1;else res+=(1^grid[i][j+1]);
        if(i==gridRowSize-1)res+=1;else res+=(1^grid[i+1][j]);
    }

    return res;
}