leetcode-463-Island-Perimeter

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描述

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:

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[[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:

分析

题目中给出了一个格子图，若干个格子连成一个小岛，图中只有一个相连的岛，且岛中没有湖，要求是统计岛的周长。

一次遍历即可。

解决方案1(Javascript)

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/**
 * @param {number[][]} grid
 * @return {number}
 */
var islandPerimeter = function(grid) {
    var result = 0;
    if (!grid.length) {
        return result;
    }
    
    var rowsNum = grid.length;
    var columnsNum = grid[0] && grid[0].length;
    for (let row = 0; row < rowsNum; row++) {
        for (let col = 0; col < columnsNum; col++) {
            if (grid[row][col] == 0) {
                continue;
            }
            if (row == 0 || grid[row-1][col] == 0) {
                result++;
            }
            if (col == 0 || grid[row][col-1] == 0) {
                result++;
            }
            if (row == rowsNum-1 || grid[row+1][col] == 0) {
                result++;
            }
            if (col == columnsNum-1 || grid[row][col+1] == 0) {
                result++;
            }
        }
    }
    return result;
};

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