Island Perimeter-优快云博客

本文介绍了一个LeetCode上的算法题目——岛屿周长的解决方案。通过分析二维网格中的岛屿形状，使用特定算法计算出岛屿的周长。

1. Title
463. Island Perimeter
2. Http address
https://leetcode.com/problems/island-perimeter/?tab=Description
3. The question

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:

4.Code

{
        
        int re = 0;
        if (grid == null || grid.length <= 0) {
            return re;
        }
        int rowLen = grid.length;
        int colLen = grid[0].length;
        boolean leftIsland = false;
        for (int i = 0; i < colLen; i++) {
            if (grid[0][i] == 1) {
                if (leftIsland) {
                    re += 2;
                } else {
                    re += 4;
                }
                leftIsland = true;
            } else {
                leftIsland = false;
            }
        }

        for (int i = 1; i < rowLen; i++) {
            leftIsland = false;
            for (int j = 0; j < colLen; j++) {
                if (grid[i][j] == 1) {
                    re += 4;
                    if (grid[i - 1][j] == 1) {
                        re -= 2;
                    }
                    if (leftIsland) {
                        re -= 2;
                    }
                    leftIsland = true;
                } else {
                    leftIsland = false;
                }
            }
        }
        return re;
    }
}