From 51e518208abd703f79cebf1fec21f162a6688dc5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=94=90=E6=A0=91=E6=A3=AE?= <14021051@buaa.edu.cn>
Date: Tue, 18 Sep 2018 23:28:02 +0800
Subject: [PATCH] Create 463. Island Perimeter.md

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+# [463. Island Perimeter](https://leetcode.com/problems/island-perimeter/description/)
+# 思路
+求”小岛”的周长，题目给了一些“小岛”的限制条件，例如小岛没有“湖”、“小岛”都是由方块上下连接的等等。  
+我们只需要遍历一遍grid，对于每个方块，根据是否是边界和周围方块的情况进行合适的周长累加即可。   
+时间复杂度O(n)
+# C++
+```
+class Solution {
+public:
+    int islandPerimeter(vector<vector<int>>& grid) {
+        int dx[4] = {1, -1, 0, 0};
+        int dy[4] = {0, 0, 1, -1};
+        int r = grid.size(), c = grid[0].size(), res = 0, x, y;
+        for(int i = 0; i < r; i++)
+            for(int j = 0; j < c; j++){
+                if(grid[i][j] == 0) continue;
+                if(i == 0) res++;
+                if(i == (r - 1)) res++;
+                if(j == 0) res++;
+                if(j == (c - 1)) res++;
+                for(int k = 0; k < 4; k++){ // 上下左右
+                    x = i + dx[k];
+                    y = j + dy[k];
+                    if(!(x < 0 || x >= r || y < 0 || y >= c) && grid[x][y] == 0) res++;   
+                }
+            }
+        return res;
+    }
+};
+```