# Leetcode 463. Island Perimeter
###### tags: `Leetcode`

題目
You are given row x col grid representing a map where grid[i][j] = 1 represents land and grid[i][j] = 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", meaning the water inside 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 1:

Input: grid = [[0,1,0,0],[1,1,1,0],[0,1,0,0],[1,1,0,0]]
Output: 16
Explanation: The perimeter is the 16 yellow stripes in the image above.
Example 2:

Input: grid = [[1]]
Output: 4
Example 3:

Input: grid = [[1,0]]
Output: 4

解法:
1.因為island只有一大塊，且都連接再一起，所以就for迴圈遍歷所有的cell即可，判斷每個cell的周圍是海還是陸地還是邊界。

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int islandPerimeter(int** grid, int gridSize, int* gridColSize){
    int res = 0;
    for(int i = 0; i < gridSize; i++)
    {
        for(int j = 0; j < gridColSize[i]; j++)
        {
            if(grid[i][j])
            {
                //add4side
                res+=4;
                
                //up
                if(i>0)
                    res-=grid[i-1][j];
                //left
                if(j>0)
                    res-=grid[i][j-1];
                //down
                if(i<gridSize-1)
                    res-=grid[i+1][j];
                //right
                if(j<gridColSize[i]-1)
                    res-=grid[i][j+1];
            }
        }
    }
    return res;
}