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Facebook Hacker Cup 2017 Round 3
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‎Facebook Hacker Cup/2017/Round3/A.java

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import java.io.*;
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import java.util.*;
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/**
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* Facebook Hacker Cup 2017 Round 3
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* Problem A. Salient Strings
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*/
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public class Main {
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public String solve(Scanner scanner) throws Exception {
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int n=scanner.nextInt();
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char[] s=new char[n];
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int[] a=new int[n+1], p=new int[n];
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for (int i=0;i<n;i++) {
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int x=scanner.nextInt()-1;
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a[i]=x; p[x]=i;
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}
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a[n]=-1;
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s[p[0]]='A';
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for (int i=1;i<n;i++) {
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if (a[p[i]+1]>a[p[i-1]+1])
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s[p[i]]=s[p[i-1]];
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else {
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if (s[p[i-1]]=='Z') return "-1";
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s[p[i]]=(char)(s[p[i-1]]+1);
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}
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}
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return new String(s);
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}
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public static void main(String[] args) throws Exception {
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System.setIn(new FileInputStream("input.txt"));
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System.setOut(new PrintStream("output.txt"));
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Scanner scanner=new Scanner(System.in);
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int times=Integer.parseInt(scanner.nextLine());
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long start=System.currentTimeMillis();
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for (int t=1;t<=times;t++) {
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try {
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System.out.println(String.format("Case #%d: %s", t, new Main().solve(scanner)));
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}
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catch (Throwable e) {
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System.err.println("ERROR in case #"+t);
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e.printStackTrace();
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}
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}
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long end=System.currentTimeMillis();
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System.err.println(String.format("Time used: %.3fs", (end-start)/1000.0));
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}
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}

‎Facebook Hacker Cup/2017/Round3/B.java

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import java.io.*;
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import java.util.*;
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/**
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* Facebook Hacker Cup 2017 Round 3
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* Problem B. Sluggish Security
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*/
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public class Main {
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private static final long MOD = 1000000007L;
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private static long[] x, y;
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public String solve(Scanner scanner) throws Exception {
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calMod();
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int n=scanner.nextInt();
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long[] a=input(scanner, n), b=input(scanner, n);
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int ai=0, bi=0;
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long ans=1;
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while (ai<n || bi<n) {
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////// CASE 1: X,X
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if (ai<n && bi<n && a[ai]==b[bi]) {
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ai++; bi++;
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}
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////// CASE 2: XY,YX
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else if (ai+1<n && bi+1<n && a[ai]==b[bi+1] && a[ai+1]==b[bi]) {
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ans*=2; ans%=MOD;
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ai+=2; bi+=2;
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}
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////// CASE 3: XYX,Y
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else if (ai+2<n && bi<n && a[ai]==a[ai+2] && a[ai+1]==b[bi]) {
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ans*=2; ans%=MOD;
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ai+=3; bi++;
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}
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////// CASE 4: X,YXY
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else if (bi+2<n && ai<n && b[bi]==b[bi+2] && b[bi+1]==a[ai]) {
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ans*=2; ans%=MOD;
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ai++; bi+=3;
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}
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////// CASE 5: XX|XYXY|...
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else {
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int al = 0, bl = 0;
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while (true) {
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if (ai+1<n && a[ai]==a[ai+1]) {
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ai+=2;
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al++;
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}
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else if (ai+3<n && a[ai]==a[ai+2] && a[ai+1]==a[ai+3]) {
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ai+=4;
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al++;
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}
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else break;
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}
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while (true) {
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if (bi+1<n && b[bi]==b[bi+1]) {
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bi+=2;
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bl++;
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}
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else if (bi+3<n && b[bi]==b[bi+2] && b[bi+1]==b[bi+3]) {
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bi+=4;
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bl++;
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}
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else break;
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}
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// Not IMPOSSIBLE
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if (al==0 && bl==0) return "0";
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ans=ans*x[al+bl]%MOD*y[al]%MOD*y[bl]%MOD;
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}
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}
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return String.valueOf(ans);
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}
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private long[] input(Scanner scanner, int n) {
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long[] a=new long[n], da=new long[n];
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a[0]=scanner.nextLong();
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int k=scanner.nextInt(), index=0;
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for (int i=0;i<k;i++) {
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int r=scanner.nextInt(), l=scanner.nextInt();
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ArrayList<Long> list=new ArrayList<>();
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for (int j=0;j<l;j++) list.add(scanner.nextLong());
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for (int j=0;j<r;j++) {
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for (long u: list) {
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a[index+1]=a[index]+u;
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index++;
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}
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}
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}
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return a;
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}
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private static void calMod() {
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if (x!=null) return;
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x=new long[5000000]; y=new long[5000000];
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// x
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x[0]=1;
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y[0]=1;
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for (int i=1;i<5000000;i++) {
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x[i]=x[i-1]*i%MOD;
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y[i]=quickPow(x[i], MOD-2);
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}
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}
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// x^n%p
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private static long quickPow(long x, long n) {
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if (n==0) return 1;
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if (n==1) return x;
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long v=quickPow(x, n/2);
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return v*v%MOD*(n%2!=0?x:1)%MOD;
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}
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public static void main(String[] args) throws Exception {
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System.setIn(new FileInputStream("input.txt"));
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System.setOut(new PrintStream("output.txt"));
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Scanner scanner=new Scanner(System.in);
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int times=Integer.parseInt(scanner.nextLine());
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long start=System.currentTimeMillis();
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for (int t=1;t<=times;t++) {
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try {
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System.out.println(String.format("Case #%d: %s", t, new Main().solve(scanner)));
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}
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catch (Throwable e) {
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System.err.println("ERROR in case #"+t);
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e.printStackTrace();
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}
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}
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long end=System.currentTimeMillis();
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System.err.println(String.format("Time used: %.3fs", (end-start)/1000.0));
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}
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}

‎README.md

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- [Qualification Round](Facebook%20Hacker%20Cup/2017/Qualification%20Round): A/B/C
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- [Round1](Facebook%20Hacker%20Cup/2017/Round1): A/B/C
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- [Round2](Facebook%20Hacker%20Cup/2017/Round2): A/D
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- [Round3](Facebook%20Hacker%20Cup/2017/Round3): A/B
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### Other Contests
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To be continued...

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