题目
Given a 2d grid map of ‘1’s (land) and ‘0’s (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.
Example 1:
11110
11010
11000
00000
Answer: 1
Example 2:
11000
11000
00100
00011
Answer: 3
思路
可以参考:Find the number of islands
有一点不同的是本题目只用考虑四个方向,而参考题目是考虑了8个方向。
代码
#include <iostream>
#include <vector>
using namespace std;
class Solution {
public:
int numIslands(vector<vector<char>> &grid) {
int row = grid.size();
if(row == 0){
return 0;
}
int col = grid[0].size();
if(col == 0){
return 0;
}
int count = 0;
for(int i = 0;i < row;++i){
for(int j = 0;j < col;++j){
if(grid[i][j] == '1'){
DFS(grid,row,col,i,j);
++count;
}
}
}
return count;
}
private:
void DFS(vector<vector<char> > &grid,int row,int col,int x,int y){
if(x < 0 || y < 0 || x >= row || y >= col || grid[x][y] == '0'){
return;
}
grid[x][y] = '0';
DFS(grid,row,col,x,y+1);
DFS(grid,row,col,x,y-1);
DFS(grid,row,col,x-1,y);
DFS(grid,row,col,x+1,y);
}
};
int main() {
Solution solution;
vector<vector<char> > grid =
{
{'1', '1', '0', '0', '0'},
{'1', '1', '0', '0', '0'},
{'0', '0', '1', '0', '0'},
{'0', '0', '0', '1', '1'}
};
cout<<solution.numIslands(grid)<<endl;
return 0;
}
运行时间
<script type="text/javascript">
$(function () {
$('pre.prettyprint code').each(function () {
var lines = $(this).text().split('\n').length;
var $numbering = $('<ul/>').addClass('pre-numbering').hide();
$(this).addClass('has-numbering').parent().append($numbering);
for (i = 1; i <= lines; i++) {
$numbering.append($('<li/>').text(i));
};
$numbering.fadeIn(1700);
});
});
</script>
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