本週題目比較簡單暴力。
1252. Cells with Odd Values in a Matrix
暴力模擬
class Solution {
public int oddCells(int n, int m, int[][] indices) {
int ans=0;
int[][] chess=new int[n][m];
for(int[] a:indices){
for(int i=0;i<m;i++)
chess[a[0]][i]+=1;
for(int i=0;i<n;i++)
chess[i][a[1]]+=1;
}
for(int i=0;i<n;i++){
for(int j=0;j<m;j++){
if((chess[i][j] & 1)==1)
ans++;
}
}
return ans;
}
}
1253. Reconstruct a 2-Row Binary Matrix
暴力方法
class Solution {
public List<List<Integer>> reconstructMatrix(int upper, int lower, int[] colsum) {
int cols=colsum.length;
int[][] nums=new int[2][cols];
ArrayList<Integer> left=new ArrayList<>();
int count=0;
for(int i=0;i<cols;i++){
if(colsum[i]==2){
nums[0][i]=1;
nums[1][i]=1;
upper--;
lower--;
}
if(colsum[i]==1){
left.add(i);
count++;
}
}
if(count!=upper+lower)
return new LinkedList<>();
for(int i=0;i<left.size();i++){
if(upper>lower){
nums[0][left.get(i)]=1;
upper--;
}
else{
nums[1][left.get(i)]=1;
lower--;
}
}
if(upper==0 && lower==0){
LinkedList<List<Integer>> ans=new LinkedList<>();
for(int i=0;i<2;i++){
LinkedList<Integer> tmp=new LinkedList<>();
for(int j=0;j<cols;j++)
tmp.add(nums[i][j]);
ans.add(tmp);
}
return ans;
}
else
{
return new LinkedList<>();
}
}
}
1254. Number of Closed Islands
經典的BFS似曾相識
class Solution {
static class Coordinate{
int x,y;
public Coordinate(int x,int y){
this.x=x;
this.y=y;
}
}
int[] dirsX={0,0,1,-1};
int[] dirsY={-1,1,0,0};
public int closedIsland(int[][] grid) {
int ans=0;
int m=grid.length,n=grid[0].length;
boolean[][] visited=new boolean[m][n];
for(int i=1;i<m-1;i++)
{
for(int j=1;j<n-1;j++)
{
if(grid[i][j]==0 && !visited[i][j])
{
boolean flag=false;
Queue<Coordinate> q=new LinkedList<>();
q.add(new Coordinate(i,j));
while(!q.isEmpty()){
Coordinate tmp=q.poll();
int x=tmp.x,y=tmp.y;
if(x==0 || x==m-1 || y==0 || y==n-1)
flag=true;
for(int k=0;k<4;k++){
int x1=x+dirsX[k],y1=y+dirsY[k];
if((x1>=0 && x1<m) && (y1>=0 && y1<n) && grid[x1][y1]==0 && !visited[x1][y1]){
visited[x1][y1]=true;
q.add(new Coordinate(x1,y1));
}
}
}
if(!flag)
ans++;
}
}
}
return ans;
}
}
1255. Maximum Score Words Formed by Letters
經典的狀態壓縮動態規劃似曾相識
class Solution {
public static boolean isChosen(int i,int j){
if(((i>>j) & 1)==1)
return true;
else
return false;
}
public static boolean canDistribute(String word,int[] curCount){
for(int i=0;i<word.length();i++){
if(curCount[word.charAt(i)-'a']>=1)
curCount[word.charAt(i)-'a']--;
else
return false;
}
return true;
}
public int maxScoreWords(String[] words, char[] letters, int[] score) {
int n=words.length;
//可選字母計數
int[] count=new int[26];
for(char c:letters){
count[c-'a']++;
}
//候選單詞得分
int[] scores=new int[n];
for(int j=0;j<words.length;j++)
{
String word=words[j];
for(int i=0;i<word.length();i++)
{
scores[j]+=score[word.charAt(i)-'a'];
}
}
int N=1<<n,ans=0;
for(int i=0;i<N;i++){
int curMax=0;
int[] curCount=new int[26];
for(int k=0;k<26;k++)
curCount[k]=count[k];
for(int j=0;j<n;j++)
{
if(isChosen(i,j))
{
if(canDistribute(words[j],curCount))
curMax+=scores[j];
else
break;
}
}
ans=Math.max(ans,curMax);
}
return ans;
}
}
1266. Minimum Time Visiting All Points
按順序訪問二維座標點，每一步只能水平、豎直、正對角移動一個單元格，對於相鄰點構成正方形的情況，所需步數爲正方形的邊長；對於矩形情況，也容易看出所需步數爲矩形長邊的長度。因此將兩條規則統一：
class Solution {
public int minTimeToVisitAllPoints(int[][] points) {
int ans=0;
for(int i=1;i<points.length;i++){
ans+=Math.max(Math.abs(points[i][0]-points[i-1][0]),Math.abs(points[i][1]-points[i-1][1]));
}
return ans;
}
}
1267. Count Servers that Communicate
能夠通信的服務器必然在同一行或者同一列，也就是說在空十字線上的服務器被忽略，類似八皇后裏面標記行列狀態的技巧，需要用行數組和列數組來記錄服務器的數量
class Solution {
public int countServers(int[][] grid) {
int[] recordRow=new int[250];
int[] recordCol=new int[250];
int m=grid.length;
int n=grid[0].length;
for(int i=0;i<m;i++){
for(int j=0;j<n;j++){
if(grid[i][j]!=0)
{
recordRow[i]++;
recordCol[j]++;
}
}
}
int ans=0;
for(int i=0;i<m;i++){
for(int j=0;j<n;j++)
{
if( grid[i][j] == 1 && ( recordRow[i]>1 || recordCol[j]>1 ))
{
//System.out.println(i+" "+j);
ans++;
}
}
}
return ans;
}
}
1268. Search Suggestions System
這個問題是Trie的加強（實現他的應用功能：拼寫提示），這裏原封不動拷貝Trie Implementation的代碼，核心代碼是對Trie的深度優先遍歷操作，對於輸入不斷增加的字母，（新）前綴的搜索定位都需要從Trie根節點開始，這一步是相對冗餘的操作，可以進一步優化。
算法一：
class Solution {
public static int count = 0;
public static int MAX = 3;
public List<List<String>> suggestedProducts(String[] products, String searchWord) {
List<List<String>> ans = new LinkedList<>();
Trie trie = new Trie();
for (int i = 0; i < products.length; i++) {
trie.insert(products[i]);
}
for (int i = 0; i < searchWord.length(); i++) {
count = 0;
String prefix = searchWord.substring(0, i + 1);
List<String> record = new LinkedList<>();
TrieNode node = trie.searchPrefix(prefix);
if(node!=null){
if(node.isEnd){
record.add(prefix);
count++;
}
collect(prefix, node, record);
}
ans.add(record);
}
return ans;
}
public void collect(String cur, TrieNode node, List<String> record) {
if (count == MAX)
return;
for (char c = 'a'; c <= 'z' && count<MAX; c++) {
if (node.containsKey(c)) {
String next = cur + c;
if (node.get(c).isEnd) {
record.add(next);
count++;
}
collect(next, node.get(c), record);
}
}
}
class TrieNode {
private TrieNode[] links;
private final int R = 26;
private boolean isEnd;
public TrieNode() {
links = new TrieNode[R];
}
public boolean containsKey(char c) {
return links[c - 'a'] != null;
}
public TrieNode get(char c) {
return links[c - 'a'];
}
public void put(char c, TrieNode node) {
links[c - 'a'] = node;
}
public void setEnd() {
isEnd = true;
}
}
class Trie {
private TrieNode root;
/**
* Initialize your data structure here.
*/
public Trie() {
root = new TrieNode();
}
/**
* Inserts a word into the trie.
*/
public void insert(String word) {
TrieNode node = root;
for (int i = 0; i < word.length(); i++) {
char curChar = word.charAt(i);
if (!node.containsKey(curChar))
node.put(curChar, new TrieNode());
node = node.get(curChar);
}
node.setEnd();
}
/*
返回以word爲前綴的Trie節點
*/
private TrieNode searchPrefix(String word) {
TrieNode node = root;
for (int i = 0; i < word.length(); i++) {
char curChar = word.charAt(i);
if (node.containsKey(curChar))
node = node.get(curChar);
else
return null;
}
return node;
}
/**
* Returns if the word is in the trie.
*/
public boolean search(String word) {
TrieNode node = searchPrefix(word);
return node != null && node.isEnd;
}
/**
* Returns if there is any word in the trie that starts with the given prefix.
*/
public boolean startsWith(String prefix) {
TrieNode node = searchPrefix(prefix);
return node != null;
}
}
/*
public static void main(String[] args) {
String[] strs = {"mobile", "mouse", "moneypot", "monitor", "mousepad"};
String searchWord = "mouse";
SearchSuggestions ss = new SearchSuggestions();
List<List<String>> ans = ss.suggestedProducts(strs, searchWord);
for (List<String> t : ans) {
for (String s : t) {
System.out.print(s + " ");
}
System.out.println();
}
}
*/
}
算法二：有點暴力匹配的意思，算法比較直觀，先按字典序排序，然後，枚舉可能的前綴與產品名一一匹配。看着複雜度比較大，實際運行起來速度挺快。
public List<List<String>> suggestedProducts(String[] products, String searchWord) {
List<List<String>> results = new ArrayList<>();
if(products == null || products.length == 0) return results;
// sort the products lexicographically
Arrays.sort(products);
for(int i = 1; i <= searchWord.length(); i++) {
List<String> temp = new ArrayList<>();
int count = 0;
for(String product : products) {
if(product.length() >= i && product.substring(0, i).equals(searchWord.substring(0, i))) {
temp.add(product);
count++;
if(count >= 3) {
break;
}
}
}
results.add(temp);
}
return results;
}
1269. Number of Ways to Stay in the Same Place After Some Steps
狀態轉移方程：
class Solution {
public static int MOD=1000000007;
public int numWays(int steps, int arrLen) {
int[] dp1=new int[arrLen+2];
dp1[1]=1;
int[] dp2=new int[arrLen+2];
int n=Math.min(steps,arrLen);
for(int i=0;i<steps;i++)
{
for(int j=1;j<n+1;j++)
dp2[j]=((dp1[j-1]+dp1[j])%MOD+dp1[j+1])%MOD;
int[] tmp=dp1;
dp1=dp2;
dp2=tmp;
}
return dp1[1];
}
}
萬年第四道不會，這該怎麼提高呀！！！
1184. Distance Between Bus Stops
class Solution {
public int distanceBetweenBusStops(int[] distance, int start, int destination) {
int dist=0,dist1=0;
if(start>destination){
int tmp=start;
start=destination;
destination=tmp;
}
for(int i=0;i<distance.length;i++){
dist+=distance[i];
if(i>=start && i<destination){
dist1+=distance[i];
}
}
return Math.min(dist-dist1,dist1);
}
}
class Solution {
public static int[][] monthLength={{31,28,31,30,31,30,31,31,30,31,30,31},{31,29,31,30,31,30,31,31,30,31,30,31}};
public static String[] symbols={"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
public static boolean isleap(int year){
if(year%4==0&&year%100!=0||year%400==0)
return true;
else
return false;
}
public String dayOfTheWeek(int day, int month, int year) {
int sum=0,cur=0;
for(int i=1971;i<year;i++){
sum+=isleap(i)?366:365;
}
if(isleap(year)){ //29天
for(int i=0;i<month-1;i++){
cur+=monthLength[1][i];
}
}
else{
for(int i=0;i<month-1;i++){
cur+=monthLength[0][i];
}
}
sum+=cur+day;
return symbols[(5+(sum-1)%7)%7];
}
}
1186. Maximum Subarray Sum with One Deletion
class Solution {
public int maximumSum(int[] arr) {
int n=arr.length;
int[] endHere=new int[n];
endHere[0]=arr[0];
int max=arr[0];
for(int i=1;i<n;i++)
{
endHere[i]=Math.max(endHere[i-1]+arr[i],arr[i]);
max=Math.max(max,endHere[i]);
}
int[] startHere=new int[n];
startHere[n-1]=arr[n-1];
for(int i=n-2;i>=0;i--){
startHere[i]=Math.max(startHere[i+1]+arr[i],arr[i]);
max=Math.max(max,startHere[i]);
}
for(int i=1;i<n-1;i++){
max=Math.max(max,endHere[i-1]+startHere[i+1]);
}
return max;
}
}