ToB企服应用市场:ToB评测及商务社交产业平台
标题:
hot100 | 九、图论
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作者:
金歌
时间:
2024-7-16 12:41
标题:
hot100 | 九、图论
1-leetcode200. 岛屿数目
注意:×
蛮奇妙的做法,直接在读取到1的时候给res的值+1,然后深度优先搜索把全部相邻的陆地全部改为海洋
注意dfs里面的范围判定,[0, **length-1]**
length-1
length-1
length-1
public int numIslands(char[][] grid) {
int res = 0;
int n = grid.length;;
int m = grid[0].length;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (grid[i][j] == '1'){
res++;
dfs(grid, i, j);
}
}
}
return res;
}
private void dfs(char[][] grid, int i, int j) {
if (i<0 || i>=grid.length || j<0 || j>=grid[0].length){
return;
}
if (grid[i][j] == '0'){
return;
}
grid[i][j] = '0';
dfs(grid, i+1, j);
dfs(grid, i, j+1);
dfs(grid, i-1, j);
dfs(grid, i, j-1);
}
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leetcode994. 腐烂的橘子
注意:×
没写,看着考的太少,懒得写了
[/code] [size=5]3-leetcode207. 课程表[/size]
注意:××
[list=1]
[*]花了许多时间,注意的地方太多了
[*]创建List<Integer>[] graph的时候,Labuladong说写代码的时候大部分都是这种连接表的格式,先创建一个LinkedList类型的数组,然后一定要注意,是graph[i] = new LinkedList<>();
[*]第二个注意的地方是有hasVisited和onPath两种记录,onPath的记录我能明确,hasVisited的记录还需要思索一下,主要的目的就是办理重复搜索
[/list] [code]
boolean hasCycle = false;
boolean[] hasVisited;
boolean[] onPath;
public boolean canFinish(int numCourses, int[][] prerequisites) {
List<Integer>[] graph = buildGraph(numCourses, prerequisites);
hasVisited = new boolean[numCourses];
onPath = new boolean[numCourses];
for (int i = 0; i < numCourses; i++) {
traverse(graph, i);
}
return !hasCycle;
}
private void traverse(List<Integer>[] graph, int i) {
if (onPath[i]){
hasCycle = true;
}
if (hasCycle || hasVisited[i]){
return;
}
hasVisited[i] = true;
onPath[i] = true;
for (Integer integer : graph[i]) {
traverse(graph, integer);
}
onPath[i] = false;
}
private List<Integer>[] buildGraph(int numCourses, int[][] prerequisites) {
List<Integer>[] graph = new LinkedList[numCourses];
for (int i = 0; i < graph.length; i++) {
graph[i] = new LinkedList<>();
}
for (int[] prerequisite : prerequisites) {
int from = prerequisite[1];
int to = prerequisite[0];
graph[from].add(to);
}
return graph;
}
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4-leetcode208. 实现 Trie (前缀树)
注意:×
看了题解再写,感觉照旧有点压力
注意isEnd的调用
class Trie {
class TrieNode{
boolean isEnd;
TrieNode[] nodes;
public TrieNode(){
isEnd = false;
nodes = new TrieNode[26];
}
}
private TrieNode root;
public Trie() {
root = new TrieNode();
}
public void insert(String word) {
TrieNode node = root;
for (char c : word.toCharArray()) {
if (node.nodes[c-'a'] == null){
node.nodes[c-'a'] = new TrieNode();
}
node = node.nodes[c-'a'];
}
node.isEnd = true;
}
public boolean search(String word) {
TrieNode node = root;
for (char c : word.toCharArray()) {
if (node.nodes[c-'a'] == null){
return false;
}
node = node.nodes[c-'a'];
}
return node.isEnd;
}
public boolean startsWith(String prefix) {
TrieNode node = root;
for (char c : prefix.toCharArray()) {
if (node.nodes[c-'a'] == null){
return false;
}
node = node.nodes[c-'a'];
}
return true;
}
}
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