代码随想录——图论一刷day03
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文章目录
- 前言
- 一、力扣130. 被围绕的区域
- 二、力扣417. 太平洋大西洋水流问题
- 三、力扣827. 最大人工岛
前言
`
一、力扣130. 被围绕的区域
class Solution {
boolean[][] flag;
int[][] move = {
{0,1},
{0,-1},
{-1,0},
{1,0}
};
public void solve(char[][] board) {
flag = new boolean[board.length][board[0].length];
for(int i = 0; i < board.length; i ++){
if(board[i][0] == 'O' && flag[i][0] == false){
dfs(board, i, 0);
}
if(board[i][board[0].length-1] == 'O' && flag[i][board[0].length-1] == false){
dfs(board, i, board[0].length-1);
}
}
for(int i = 0; i < board[0].length; i ++){
if(board[0][i] == 'O' && flag[0][i] == false){
dfs(board, 0, i);
}
if(board[board.length-1][i] == 'O' && flag[board.length-1][i] == false){
dfs(board, board.length-1, i);
}
}
for(int i = 0; i < board.length; i ++){
for(int j = 0; j < board[0].length; j ++){
if(board[i][j] == 'O' && flag[i][j] == false){
board[i][j] = 'X';
}
}
}
}
public void dfs(char[][] board, int x, int y){
flag[x][y] = true;
for(int i = 0; i < 4; i ++){
int nextX = x + move[i][0];
int nextY = y + move[i][1];
if(nextX < 0 || nextX >= board.length || nextY < 0 || nextY >= board[x].length || flag[nextX][nextY] == true || board[nextX][nextY] == 'X'){
continue;
}
dfs(board, nextX, nextY);
}
}
}
二、力扣417. 太平洋大西洋水流问题
class Solution {
int[][] move = {{0,1},{0,-1},{-1,0},{1,0}};
boolean[][][] flag;
// boolean[][] visited;
public List<List<Integer>> pacificAtlantic(int[][] heights) {
List<List<Integer>> res = new ArrayList<>();
int row = heights.length, col = heights[0].length;
flag = new boolean[row][col][2];
// visited = new boolean[row][col];
for(int i = 0; i < row; i ++){
if(flag[i][0][0] == false){
dfs(heights, i, 0, 0);
}
if(flag[i][col-1][1] == false){
dfs(heights, i, col-1, 1);
}
}
for(int i = 0; i < col; i ++){
if(flag[0][i][0] == false){
dfs(heights, 0, i, 0);
}
if(flag[row-1][i][1] == false){
dfs(heights, row-1, i, 1);
}
}
for(int i = 0; i < row; i ++){
for(int j = 0; j < col; j ++){
if(flag[i][j][0] == true && flag[i][j][1] == true){
res.add(Arrays.asList(i,j));
}
}
}
return res;
}
public void dfs(int[][] heights, int x, int y, int t){
if(t == 0){
flag[x][y][0] = true;
}else{
flag[x][y][1] = true;
}
for(int i = 0; i < 4; i ++){
int nextX = x + move[i][0];
int nextY = y + move[i][1];
if(nextX < 0 || nextX >= heights.length || nextY < 0 || nextY >= heights[x].length || heights[nextX][nextY] < heights[x][y]){
continue;
}
if(t == 0 && flag[nextX][nextY][0]){
continue;
}
if(t == 1 && flag[nextX][nextY][1]){
continue;
}
dfs(heights, nextX, nextY, t);
}
}
}
三、力扣827. 最大人工岛
class Solution {
int[][] move = {{0,1},{0,-1},{-1,0},{1,0}};
int count;
public int largestIsland(int[][] grid) {
int res = 0;
int path = 0;
int mark = 1;
Map<Integer,Integer> map = new HashMap<>();
for(int i = 0; i < grid.length; i ++){
for(int j = 0; j < grid[0].length; j ++){
if(grid[i][j] == 1){
count = 0;
mark ++;
dfs1(grid, i, j, mark);
map.put(mark,count);
res = Math.max(res,count);
}
}
}
for(int i = 0; i < grid.length; i ++){
for(int j = 0; j < grid[0].length; j ++){
if(grid[i][j] == 0){
Set<Integer> set = new HashSet<>();
path = 0;
for(int t = 0; t < 4; t ++){
int nextX = i + move[t][0];
int nextY = j + move[t][1];
if(nextX < 0 || nextX >= grid.length || nextY < 0 || nextY >= grid[0].length ||grid[nextX][nextY] == 0){
continue;
}
set.add(grid[nextX][nextY]);
}
for(Integer in : set){
path += map.get(in);
}
path += 1;
res = Math.max(res, path);
}
}
}
return res;
}
public void dfs1(int[][] grid, int x, int y, int mark){
count ++;
grid[x][y] = mark;
for(int i = 0; i < 4; i ++){
int nextX = x + move[i][0];
int nextY = y + move[i][1];
if(nextX < 0 || nextX >= grid.length || nextY < 0 || nextY >= grid[0].length || grid[nextX][nextY] == 0 || grid[nextX][nextY] == mark){
continue;
}
dfs1(grid, nextX, nextY, mark);
}
}
}