0463. Island Perimeter
https://leetcode.com/problems/island-perimeter
Description
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
Constraints:
row == grid.length
col == grid[i].length
1 <= row, col <= 100
grid[i][j]
is0
or1
.
ac
class Solution {
int peri = 0;
public int islandPerimeter(int[][] grid) {
// edge cases
if (grid.length == 0 || grid[0].length == 0) return 0;
for (int r = 0; r < grid.length; r++) {
for (int c = 0; c < grid[0].length; c++) {
if (grid[r][c] == 1) {
helper(grid, r, c);
}
}
}
return peri;
}
private void helper(int[][] grid, int row, int col) {
// exit
if (row < 0 || row >= grid.length || col < 0 || col >= grid[0].length
|| grid[row][col] == 0) {
// out of boundary
peri++;
return;
}
if (grid[row][col] == -1) return; // visited before
// look around
grid[row][col] = -1; // marked visited
helper(grid, row+1, col);
helper(grid, row-1, col);
helper(grid, row, col+1);
helper(grid, row, col-1);
}
}
/*
DFS/BFS, when meet unavailable cell perimeter++;
*/
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