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题目地址：

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.

例子：

[[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:

题目比较简单，每有一个方块边就增加4条，每有一个相邻的方块，边就减少两条，判断好边界就没问题了。

下面是该题目的Java代码实现：

public int islandPerimeter(int[][] grid) {    int perimeter = 0;    for (int i = 0; i < grid.length; i++) {        for (int j = 0; j < grid[i].length; j++) {            if (grid[i][j] == 0) {                continue;            }            if (grid[i][j] == 1) {                perimeter += 4;                if (i > 0 && grid[i - 1][j] == 1)                    perimeter -= 2;                if (j > 0 && grid[i][j - 1] == 1)                    perimeter -= 2;            }        }    }    return perimeter;}