2018-09-18 15:28:02 +00:00
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# [463. Island Perimeter](https://leetcode.com/problems/island-perimeter/description/)
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# 思路
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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。
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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。
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时间复杂度O(n)
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# C++
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2019-09-13 15:08:41 +00:00
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```C++
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2018-09-18 15:28:02 +00:00
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class Solution {
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public:
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int islandPerimeter(vector<vector<int>>& grid) {
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int dx[4] = {1, -1, 0, 0};
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int dy[4] = {0, 0, 1, -1};
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int r = grid.size(), c = grid[0].size(), res = 0, x, y;
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for(int i = 0; i < r; i++)
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for(int j = 0; j < c; j++){
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if(grid[i][j] == 0) continue;
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if(i == 0) res++;
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if(i == (r - 1)) res++;
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if(j == 0) res++;
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if(j == (c - 1)) res++;
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for(int k = 0; k < 4; k++){ // 上下左右
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x = i + dx[k];
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y = j + dy[k];
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if(!(x < 0 || x >= r || y < 0 || y >= c) && grid[x][y] == 0) res++;
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}
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}
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return res;
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}
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};
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```
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