题目

463. 岛屿的周长

解法

依题遍历陆地的四个边，如果靠近水，那么算到周长里面，否则不算

<?php

class Solution {
    
    /**
     * @param Integer[][] $grid
     * @return Integer
     */
    function islandPerimeter($grid) {
        if (empty($grid)) {
            return 0;
        }
        
        $per = 0;
        foreach ($grid as $rowKey => $rowGrid) {
            foreach ($rowGrid as $colKey => $colItem) {
                if ($colItem != 1) {
                    continue;
                }
                $per += intval(!isset($grid[$rowKey - 1][$colKey]) || $grid[$rowKey - 1][$colKey] == 0);
                $per += intval(!isset($grid[$rowKey][$colKey + 1]) || $grid[$rowKey][$colKey + 1] == 0);
                $per += intval(!isset($grid[$rowKey + 1][$colKey]) || $grid[$rowKey + 1][$colKey] == 0);
                $per += intval(!isset($grid[$rowKey][$colKey - 1]) || $grid[$rowKey][$colKey - 1] == 0);
            }
        }
        
        return $per;
    }
}

还有一种深度遍历的方式

class Solution {
    
    /**
     * @param Integer[][] $grid
     * @return Integer
     */
    function islandPerimeter($grid) {
        if (empty($grid)) {
            return 0;
        }
        
        $per = 0;
        foreach ($grid as $rowKey => $rowGrid) {
            foreach ($rowGrid as $colKey => $colItem) {
                if ($grid[$rowKey][$colKey] == 1) {
                    $per += $this->dfs($grid, $rowKey, $colKey);
                }
            }
        }
        
        return $per;
    }
    
    public function dfs(&$grid, $rowKey, $colKey) {
        if (!isset($grid[$rowKey][$colKey])) {
            return 0;
        }
        
        if ($grid[$rowKey][$colKey] == 0) {
            return 0;
        }
        
        if ($grid[$rowKey][$colKey] == 2) {
            return 0;
        }
        
        $grid[$rowKey][$colKey] = 2;
        
        $per = 0;
        $per += intval(!isset($grid[$rowKey - 1][$colKey]) || $grid[$rowKey - 1][$colKey] == 0);
        $per += intval(!isset($grid[$rowKey][$colKey + 1]) || $grid[$rowKey][$colKey + 1] == 0);
        $per += intval(!isset($grid[$rowKey + 1][$colKey]) || $grid[$rowKey + 1][$colKey] == 0);
        $per += intval(!isset($grid[$rowKey][$colKey - 1]) || $grid[$rowKey][$colKey - 1] == 0);
        
        $per += $this->dfs($grid, $rowKey - 1, $colKey);
        $per += $this->dfs($grid, $rowKey, $colKey + 1);
        $per += $this->dfs($grid, $rowKey + 1, $colKey);
        $per += $this->dfs($grid, $rowKey, $colKey - 1);
        return $per;
    }
}