Hi there! Couple of days ago I was solving problem 796C-Bank Hacking. I came up with O(nlog(n)) order solution, but it failed with Time Limit Exceeded status. The max input size was 3*10^5, which implies that order O(n*log(n)) algorithm must fit into time limit. The tutorial for the contest also mentioned the same order solution. After a few hours of debugging, I have realized that the problem is in input reading part. Well, my code used built in BufferedReader in java:

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int n =  Integer.parseInt(br.readLine());
Bank banks[] = new Bank[n];
String tokens[] = br.readLine().split(" ");
List<Integer> g[] = new List[n];	
int max = Integer.MIN_VALUE;	
for(int i =0 ;i<n;i++) {
	g[i] = new ArrayList<>();	
	int val = Integer.parseInt(tokens[i]);
	max = Math.max(max, val);			
	banks[i] = new Bank(i, val);
}		
for(int i = 0;i<n-1;i++){
	tokens = br.readLine().split(" ");
	int a = Integer.parseInt(tokens[0])-1;
	int b = Integer.parseInt(tokens[1])-1;
	g[a].add(b);
	g[b].add(a);
}

The code slice already consumed about 800 ms for the maximum size input. After I have submitted a linear time alternative solution, but I still decided to find more faster way of reading. I have found williamfiset 's InputReader which claimed to be much faster than the BufferedReader. Finally I decided to write my own FastScanner inspired with his idea. Well here it is (Currently I have just implemented it for Integers):

import java.io.*;
import java.util.*;

public class FastScanner {

    static final int DEFAULT_BUFF = 1024, EOF = -1, INT_MIN = 48, INT_MAX = 57;
    static final byte NEG = 45;
    static final int[] ints = new int[58];

    static {
        int value = 0;
        for (int i = 48; i < 58; i++) {
            ints[i] = value++;
        }
    }

    InputStream stream;

    byte[] buff;
    int buffPtr;

    public FastScanner(InputStream stream) {
        this.stream = stream;
        this.buff = new byte[DEFAULT_BUFF];
        this.buffPtr = -1;
    }

    public int nextInt() throws IOException {
        int val = 0;
        int sign = readNonDigits();
        while (isDigit(buff[buffPtr]) && buff[buffPtr] != EOF) {
            val = (val << 3) + (val << 1) + ints[buff[buffPtr]];
            buffPtr++;
            if (buffPtr == buff.length) {
                updateBuff();
            }
        }
        return val*sign;
    }

    private int readNonDigits() throws IOException {
        if (buffPtr == -1 || buffPtr == buff.length) {
            updateBuff();
        }
        if (buff[buffPtr] == EOF) {
            throw new IOException("End of stream reached");
        }
        int signByte = -1;
        while (!isDigit(buff[buffPtr])) {
            signByte = buff[buffPtr];
            buffPtr++;
            if (buffPtr >= buff.length) {
                updateBuff();
            }
            if (buff[buffPtr] == EOF) {
                throw new IOException("End of stream reached");
            }
        }
        if(signByte == NEG) return -1;
        return 1;
    }

    public void close() throws IOException {
        stream.close();
    }

    private boolean isDigit(int b) {
        return b >= INT_MIN && b <= INT_MAX;
    }

    private void updateBuff() throws IOException {
        buffPtr = 0;
        stream.read(buff);
    }
}

The FastScanner class in my code worked very fast and the maximum size input reading time has reduced up to 47 ms. As a result I have got accepted even with O(nlog(n)) order solution, just by replacing the reading part by the following code slice:

FastScanner in = new FastScanner(System.in);
int n =  in.nextInt();
Bank banks[] = new Bank[n];
List<Integer> g[] = new List[n];	
for(int i =0 ;i<n;i++) {
	g[i] = new ArrayList<>();	
	int val = in.nextInt();;
	banks[i] = new Bank(i, val+2);
}		
for(int i = 0;i<n-1;i++){
	int a = in.nextInt()-1;
	int b = in.nextInt()-1;
	g[a].add(b);
	g[b].add(a);
}

You may find my last submission here if you want.

Further I plan to upgrade and test my FastScanner, and never use BufferedReader when fast reading is important.

Thank you for attention.