island-perimeter.cpp

// Time:  O(m * n)
// Space: O(1)

class Solution {
public:
    int islandPerimeter(vector<vector<int>>& grid) {
        int count = 0, repeat = 0;
        for (int i = 0; i < grid.size(); ++i) {
            for (int j = 0; j < grid[i].size(); ++j) {
                if (grid[i][j] == 1) {
                    ++count;
                    if (i != 0 && grid[i - 1][j] == 1) {
                        ++repeat;
                    }
                    if (j != 0 && grid[i][j - 1] == 1) {
                        ++repeat;
                    }
                }
            }
        }
        return 4 * count - 2 * repeat;
    }
};