代码随想三刷图论篇2
- [104. 建造最大岛屿](#104. 建造最大岛屿)
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- [110. 字符串接龙](#110. 字符串接龙)
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- [105. 有向图的完全可达性](#105. 有向图的完全可达性)
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- [106. 岛屿的周长](#106. 岛屿的周长)
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104. 建造最大岛屿
题目
链接
代码
import java.util.*;
class Main{
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();//行
int M = sc.nextInt();//列
int[][] pic = new int[N][M];
used = new boolean[N][M];
for(int i =0;i<N;i++){
for(int j =0;j<M;j++){
pic[i][j] = sc.nextInt();
if(pic[i][j]==0){
used[i][j] = true;
}
}
}
int maxCount = 0;
int index = 1;
Map<Integer,Integer> map = new HashMap();
for(int i =0;i<N;i++){
for(int j =0;j<M;j++){
if(pic[i][j]==1){
list.clear();
dfs(pic,i,j);
for(int k = 0;k<list.size();k++){
int[] temp= list.get(k);
pic[temp[0]][temp[1]] = index;
}
map.put(index,list.size());
maxCount = Math.max(maxCount,list.size());
index++;
}
}
}
for(int i =0;i<N;i++){
for(int j =0;j<M;j++){
if(pic[i][j]==0){
Set<Integer> sett = new HashSet();
int count = 1;
if(i>=1 && !sett.contains(pic[i-1][j])){
count+=map.getOrDefault(pic[i-1][j],0);
sett.add(pic[i-1][j]);
}
if(j>=1 && !sett.contains(pic[i][j-1])){
count+=map.getOrDefault(pic[i][j-1],0);
sett.add(pic[i][j-1]);
}
if(i<pic.length-1 && !sett.contains(pic[i+1][j])){
count += map.getOrDefault(pic[i+1][j],0);
sett.add(pic[i+1][j]);
}
if(j<pic[0].length-1 && !sett.contains(pic[i][j+1])){
count+=map.getOrDefault(pic[i][j+1],0);
sett.add(pic[i][j+1]);
}
maxCount = Math.max(maxCount,count);
}
}
}
System.out.println(maxCount);
}
static boolean[][] used;
static List<int[]> list = new ArrayList();
public static void dfs(int[][] pic,int i,int j){
if(i<0||j<0||i>=pic.length||j>=pic[0].length||used[i][j]){
return;
}
used[i][j] = true;
list.add(new int[]{i,j});
if(i>=1){
dfs(pic,i-1,j);
}
if(j>=1){
dfs(pic,i,j-1);
}
if(i<pic.length-1){
dfs(pic,i+1,j);
}
if(j<pic[0].length-1){
dfs(pic,i,j+1);
}
}
}
110. 字符串接龙
题目
链接
代码
import java.util.*;
class Main{
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
int N = Integer.valueOf(sc.nextLine());
String beginStr = sc.next();
String endStr = sc.next();
Set<String> strList = new HashSet();
for(int i = 0;i<N;i++){
strList.add(sc.next());
}
int count = 0;
Deque<String> queue = new LinkedList();
queue.addLast(beginStr);
while(!queue.isEmpty()){
count++;
int size = queue.size();
for(int step = 0;step<size;step++){
String word = queue.removeFirst();
for(int i=0;i< word.length();i++){
char[] chars = word.toCharArray();
for(char k = 'a';k<='z';k++){
chars[i] = k;
String newWord = String.valueOf(chars);
if(newWord.equals(endStr)){
System.out.println(count+1);
return;
}
if(strList.contains(newWord)){
strList.remove(newWord);
queue.addLast(newWord);
}
}
}
}
}
System.out.println(0);
}
}
105. 有向图的完全可达性
题目
链接
代码
import java.util.*;
class Main{
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();
int K = sc.nextInt();
Map<Integer,Set<Integer>> map = new HashMap();
for(int i =1;i<=N;i++){
map.put(i,new HashSet());
}
for(int i = 0;i<K;i++){
int num1 = sc.nextInt();
int num2 = sc.nextInt();
map.get(num1).add(num2);
}
used = new boolean[N+1];
dfs(map,1);
for(int i =1;i<=N;i++){
if(!used[i]){
System.out.println(-1);
return;
}
}
System.out.println(1);
}
static boolean[] used;
public static void dfs(Map<Integer,Set<Integer>> map,int key){
if(used[key]){
return;
}
used[key] = true;
Set<Integer> set =map.get(key);
for(int nextNum:set){
dfs(map,nextNum);
}
}
}
106. 岛屿的周长
题目
链接
代码
import java.util.*;
class Main{
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();
int M = sc.nextInt();
int[][] pic = new int[N][M];
for(int i=0;i<N;i++){
for(int j=0;j<M;j++){
pic[i][j] = sc.nextInt();
}
}
int sum = 0; // 陆地数量
int cover = 0; // 相邻数量
for (int i = 0; i < N; i++) {
for (int j = 0; j < M; j++) {
if (pic[i][j] == 1) {
sum++; // 统计总的陆地数量
// 统计上边相邻陆地
if(i - 1 >= 0 && pic[i - 1][j] == 1) cover++;
// 统计左边相邻陆地
if(j - 1 >= 0 && pic[i][j - 1] == 1) cover++;
// 为什么没统计下边和右边？ 因为避免重复计算
}
}
}
System.out.println(sum * 4 - cover * 2 );
}
}