wfwei’s gists

wfwei / gist:5012660

Last active December 14, 2015 02:19

Java generic based on erasure, so only Object are available at runtime

	class Father {}
	class Child extends Father {}

	public class Test {
	public static void main(String args[]){
	Class<Child> cClass = Child.class;
	Class<? super Child> fClass = cClass.getSuperclass();
	// This won't compile
	// Class<Father> father = fClass.newInstance();
	//only produces Object:

wfwei / gist:5013647

Last active December 14, 2015 02:29

Basic C Grammar

	#include "stdio.h"
	#include "string"

	//宏定义方法，注意括号
	#define MAX(x,y) ((x)>(y) ? (x) :(y))
	#define IS_EVEN(n) ((n)%2==0)


	char * invalidPointer(){
	char a[100]; //栈内变量，函数返回后消亡

wfwei / gist:5023092

Last active December 14, 2015 03:39

How To Write Recursive Programs-----Don't compute anything more than once

	long int Fib(int N){
	if(N<=1)
	return 1;
	else{
	return Fib(N-1)+Fib(N-2);
	}
	}

	/**
	running time of Fib(N):

wfwei / gist:5036528

Last active December 14, 2015 05:39

Prime

	#include "stdio.h"
	#include "math.h"

	#define MAX 100000000
	int prime[MAX]; //在堆上，自动初始化为0


	void initPrimes(){
	int i, j;
	prime[0] = prime[1] = -1; // not prime number

wfwei / gist:5070689

Created March 2, 2013 11:59

Callable & Future

	import java.util.concurrent.Callable;
	import java.util.concurrent.ExecutionException;
	import java.util.concurrent.ExecutorService;
	import java.util.concurrent.Executors;
	import java.util.concurrent.Future;

	public class CallableAndFuture {

	/**
	* @param args

wfwei / gist:5237380

Last active December 15, 2015 09:19

启动三个线程，id分别是0,1,2，输出012012012

	public class ThreeThread {
	public static Long count = new Long(0);

	public static void main(String args[]) {
	for (int i = 0; i < 3; i++) {
	Thread t = new Thread() {
	@Override
	public void run() {
	int c = 3;
	while (c>0)

wfwei / gist:5237595

Created March 25, 2013 14:44

Fib...

	package mine.old.staff;

	public class Fib {
	static final int MAX = 93;
	static long[] f = new long[MAX];
	static {
	f[0] = 0;
	f[2] = f[1] = 1;
	}

wfwei / gist:5656636

Created May 27, 2013 11:46

求连续子数组的最大和题目详情: 一个整型数组，数组里有正数也有负数。数组中连续的一个或多个整数组成一个子数组，每个子数组都有一个和，求所有子数组的和的最大值，要求时间复杂度为O(n)。例如输入的数组为1, -2, 3, 10, -4, 7, 2, -5，那么最大的子数组为3, 10, -4, 7, 2，因此输出为该子数组的和18，请完成函数int MaxSum(int* a,int n)。答题说明: 当全是负数的情况时，返回最大的那个负数

	int MaxSum(int* a,int n)
	{
	int i=0, maxSum=1<<31, sum=0;
	while(i<n){
	sum += a[i++];
	if(sum>maxSum)
	maxSum = sum;
	if(sum<0)
	sum = 0;
	}

wfwei / gist:5669286

Last active December 17, 2015 20:39

字符串转换成整数题目详情: 输入一个表示整数的字符串，把该字符串转换成整数并输出。例如输入字符串"345"，则输出整数345。

	// more smarter way to solve overflow problem
	int StrToInt(const char* str)
	{
	//int maxAbs=((unsigned int)~0)>>1,maxAbsDiv=maxAbs/10, maxAbsRem=maxAbs%10;
	int maxAbs=0x7FFFFFFF,maxAbsDiv=maxAbs/10, maxAbsRem=maxAbs%10;
	int val=0, i=0, sign=1;
	while(str[i]==' ')
	i++;
	if(str[i]=='-' \|\| str[i]=='+'){
	if(str[i]=='-'){

wfwei / gist:5702713

Created June 4, 2013 00:36

Berkeley DB usage example

	package mine.code.snippet.db;

	import java.io.File;
	import java.util.ArrayList;
	import java.util.List;

	import com.sleepycat.je.Cursor;
	import com.sleepycat.je.Database;
	import com.sleepycat.je.DatabaseConfig;
	import com.sleepycat.je.DatabaseEntry;

WangFengwei wfwei