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LeetCode200.java
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142 lines (135 loc) · 4.22 KB
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package problems;
import java.util.LinkedList;
import java.util.Queue;
/**
* DFS
*/
public class LeetCode200 {
public int numIslands(char[][] grid) {
if(grid == null || grid.length == 0) {
return 0;
}
int row = grid.length;
int col = grid[0].length;
int numIsLands = 0;
for (int i = 0; i < row; i++) {
for (int j = 0; j < col; j++) {
if(grid[i][j] == '1') {
numIsLands ++;
dfs(grid, i, j);
}
}
}
return numIsLands;
}
private void dfs(char[][] grid, int i, int j) {
int row = grid.length;
int col = grid[0].length;
if(i < 0 || j < 0 || i >= row || j >= col || grid[i][j] == 0) {
return;
}
grid[i][j] = '0';
dfs(grid, i - 1, j);
dfs(grid, i + 1, j);
dfs(grid, i, j - 1);
dfs(grid, i, j + 1);
}
}
/**
* BFS
*/
class LeetCode200_1 {
public int numIslands(char[][] grid) {
if (grid == null || grid.length == 0) {
return 0;
}
int nr = grid.length;
int nc = grid[0].length;
int numIsLands = 0;
for (int r = 0; r < nr; ++r) {
for (int c = 0; c < nc; ++c) {
if (grid[r][c] == '1') {
++numIsLands;
grid[r][c] = '0';
Queue<Integer> neighbors = new LinkedList<>();
neighbors.add(r * nc + c);
while (!neighbors.isEmpty()) {
int id = neighbors.remove();
int row = id / nc;
int col = id % nc;
if (row - 1 >= 0 && grid[row-1][col] == '1') {
neighbors.add((row-1) * nc + col);
grid[row-1][col] = '0';
}
if (row + 1 < nr && grid[row+1][col] == '1') {
neighbors.add((row+1) * nc + col);
grid[row+1][col] = '0';
}
if (col - 1 >= 0 && grid[row][col-1] == '1') {
neighbors.add(row * nc + col-1);
grid[row][col-1] = '0';
}
if (col + 1 < nc && grid[row][col+1] == '1') {
neighbors.add(row * nc + col+1);
grid[row][col+1] = '0';
}
}
}
}
}
return numIsLands;
}
}
/**
* 扩展题：关于求岛屿中哪个岛屿面积最大的问题？
*/
class LeetCode_special {
static int num = 0;
public static int maxAreaOfIsland(int[][] grid) {
/**
* 只存值为1的元素是否访问
*/
boolean[][] isVisited = new boolean[grid.length][grid[0].length];
int result = 0;
for (int i = 0; i < grid.length; i++) {
for (int j = 0; j < grid[0].length; j++) {
if (grid[i][j] == 0){
continue;
}
if (isVisited[i][j]){
continue;
}
num = 0;
int len = dfs(grid, i, j, isVisited);
result = Math.max(len,result);
}
}
return result;
}
private static int dfs(int[][] grid, int i, int j, boolean[][] isVisited) {
int row = grid.length;
int col = grid[0].length;
if (isVisited[i][j]){
return 0;
}
isVisited[i][j] = true;
num++;
//上
if (i - 1 >= 0 && !isVisited[i - 1 ][j] && grid[i - 1][j] == 1){
dfs(grid,i - 1 , j, isVisited);
}
//右
if (j + 1 < col && !isVisited[i][j + 1] && grid[i][j + 1] == 1){
dfs(grid,i , j + 1, isVisited);
}
//下
if (i + 1 < row && !isVisited[i + 1][j] && grid[i + 1][j] == 1){
dfs(grid,i + 1, j, isVisited);
}
//左
if (j - 1 >= 0 && !isVisited[i][j - 1] && grid[i][j -1] == 1){
dfs(grid, i, j - 1 , isVisited);
}
return num;
}
}