Number of Islands

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Total Accepted: 96206
Total Submissions: 288576
Difficulty: Medium
Contributor: LeetCode

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:

Answer: 1

Example 2:

Answer: 3

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

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Java

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publicclass Solution {
publicint numIslands(char[][] grid) {
intres=0;
for(inti=0;i<grid.length;i++)
for(intj=0;j<grid[0].length;j++)
if(grid[i][j]=='1'){
res++;
bfs(grid,i,j);
}
returnres;
}
publicvoid bfs(char[][] grid,int x,int y){
LinkedList<int[]>que=newLinkedList<int[]>();
que.addLast(newint[]{x,y});
int[][]f={{1,0},{-1,0},{0,1},{0,-1}};
grid[x][y]='0';
while(!que.isEmpty()){
int[]cur=que.pollFirst();
for(int[]ff:f){
intr=cur[0]+ff[0];
intc=cur[1]+ff[1];
if(r>=0&&r<grid.length&&c>=0&&c<grid[0].length&&grid[r][c]=='1'){
grid[r][c]='0';
que.addLast(newint[]{r,c});
}
}
}
}
}

时间复杂度：O(N*M)

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