zoukankan      html  css  js  c++  java
  • LeetCode 694. Number of Distinct Islands

    原题链接在这里:https://leetcode.com/problems/number-of-distinct-islands/description/

    题目:

    Given a non-empty 2D array grid of 0's and 1's, an island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water.

    Count the number of distinct islands. An island is considered to be the same as another if and only if one island can be translated (and not rotated or reflected) to equal the other.

    Example 1:

    11000
    11000
    00011
    00011
    

    Given the above grid map, return 1.

    Example 2:

    11011
    10000
    00001
    11011

    Given the above grid map, return 3.

    Notice that:

    11
    1
    

    and

     1
    11
    

    are considered different island shapes, because we do not consider reflection / rotation.

    Note: The length of each dimension in the given grid does not exceed 50.

    题解:

    对每个为1的点进行dfs, 同时记下做过的path. 看最后做过多少种不同的path.

    Note: dfs每层最后要加分割的数字, 不然不能确定step是在哪个level走的. 

    e.g. 1-1-1    和  1-1       如果不加分割数字走出的path是相同的.

          |                |

             1            1- 1 

    Time Complexity: O(m*n). m = grid.length. n = grid[0].length.

    Space: O(m*n). stack space.

    AC Java:

     1 class Solution {
     2     public int numDistinctIslands(int[][] grid) {
     3         if(grid == null || grid.length == 0 || grid[0].length == 0){
     4             return 0;
     5         }
     6         
     7         HashSet<List<Integer>> shapes = new HashSet<List<Integer>>();
     8         for(int i = 0; i<grid.length; i++){
     9             for(int j = 0; j<grid[0].length; j++){
    10                 if(grid[i][j] == 1){
    11                     List<Integer> shape = new ArrayList<Integer>();
    12                     dfs(grid, i, j, shape, 0);
    13                     shapes.add(shape);
    14                 }
    15             }
    16         }
    17         
    18         return shapes.size();
    19     }
    20     
    21     private void dfs(int[][] grid, int i, int j, List<Integer> shape, int direction){
    22         if(i<0 || i>=grid.length || j<0 || j>=grid[0].length || grid[i][j]!=1){
    23             return;
    24         }
    25         
    26         grid[i][j] = 0;
    27         shape.add(direction);
    28         dfs(grid, i-1, j, shape, 1);
    29         dfs(grid, i+1, j, shape, 2);
    30         dfs(grid, i, j-1, shape, 3);
    31         dfs(grid, i, j+1, shape, 4);
    32         
    33         shape.add(0);
    34     }
    35 }

    类似Number of Islands.

  • 相关阅读:
    第三周作业
    第二周作业
    第一次作业(2)
    第一次作业
    百度翻译新API C#版在 winform,Asp.Net的小程序
    ajax 里的数据请求
    结合css与javascript来实现手机移动端的屏幕滑动效果
    js公农历互转(1900~2100年)
    webpack命令
    vscode快速输出console.log
  • 原文地址:https://www.cnblogs.com/Dylan-Java-NYC/p/7927002.html
Copyright © 2011-2022 走看看