5303. 解码字母到整数映射
写代码的过程中有两个地方没注意到，一直在改BUG
1、int 和char转换，自然是想到Integer.parseInt，但是这个方法前提是要将char转换成String，char转String，用String.valueOf()
2、还有 char类型和Int类型相加时，会默认转换为int类型，所以如果要赋值给char要进行强制转换
3、String类的一些常用方法，当没有使用IDE写代码的时候，这些常用方法老是写错了，比如substring()
class Solution {
public String freqAlphabets(String s) {
StringBuilder res =new StringBuilder();
if(null==s|| 0==s.length()){
return null;
}
int left =0;
int right = 1;
int count = 0;
while(left<s.length()){
while(right<s.length() && s.charAt(right)!='#'){
right++;
}
if(right>=s.length()){
break;
}
while(right-left>2){
count = Integer.parseInt(String.valueOf(s.charAt(left)))-1;
char temp = (char)('a'+count);
res.append(temp);
left++;
}
if(right-left==2){
count = Integer.parseInt(s.substring(left,right)) -1;
char temp =(char)('a'+count);
res.append(temp);
left= right+1;
right= left+1;
}
}
while(left<s.length()){
count = Integer.parseInt(String.valueOf(s.charAt(left)))-1;
char temp = (char)('a'+count);
res.append(temp);
left++;
}
return new String(res);
}
}
5304. 子数组异或查询
class Solution {
public int[] xorQueries(int[] arr, int[][] queries) {
int length = queries.length;
int [] res = new int[length];
for(int i=0;i<length;i++){
int left = queries[i][0];
int right = queries[i][1];
int temp = arr[left];
for(int j= left+1;j<=right;j++){
temp ^= arr[j];
}
res[i]=temp;
}
return res;
}
}
5305. 获取你好友已观看的视频
Collection.sort中重写compare的方法不太熟悉，花了很长时间
然后Entry老是提示cannot find symbol class entry，后来Import一下库就好了，之前想了半天不知道错在哪里。
题目想法是简单的，主要是卡在排序那儿了，没想出更好的办法。
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Queue;
class Solution {
boolean [] visited = null;
public List<String> watchedVideosByFriends(List<List<String>> watchedVideos, int[][] friends, int id, int level) {
int length = friends.length;
visited = new boolean[length];
//获取第K层的好友
visited[id] = true;
Queue<Integer> q = new LinkedList<Integer>();
q.offer(id);
int[] eachQcount = new int[level+1];
eachQcount[0] = 1;
for(int i=1;i<=level;i++){
for(int count = 0;count < eachQcount[i-1];count++ ){
int [] currFriends = friends[q.poll()];
for(int j =0 ;j<currFriends.length;j++){
if(visited[currFriends[j]]==false){
q.offer(currFriends[j]);
visited[currFriends[j]] = true;
eachQcount[i]++;
}
}
}
}
//获取k层朋友的播放列表，并排序
Map<String,Integer> maps = new HashMap<String,Integer>();
while(!q.isEmpty()){
int index = q.poll();
List<String> videoList = watchedVideos.get(index);
for(int i =0 ;i<videoList.size();i++){
if(maps.containsKey(videoList.get(i))){
maps.put(videoList.get(i),maps.get(videoList.get(i))+1);
}else{
maps.put(videoList.get(i),1);
}
}
}
List<Map.Entry<String,Integer>> lists = new ArrayList<Map.Entry<String,Integer>>(maps.entrySet());
Collections.sort(lists,new Comparator<Map.Entry<String,Integer>>(){
@Override
public int compare(Entry<String, Integer> o1,
Entry<String, Integer> o2) {
// TODO Auto-generated method stub
if (o1.getValue().intValue() == o2.getValue().intValue()) {
return o1.getKey().compareTo(o2.getKey());
} else {
return o1.getValue() - o2.getValue();
}
}
});
List<String> res = new ArrayList<String>();
for(Entry<String,Integer> e:lists){
// System.out.println("s: "+s+" ");
res.add(e.getKey());
}
return res;
}
}
今天在第三题中卡太久，第四题还是没写。There is a long way to go.
