将数组的奇数移到前面偶数到后面&&输出链表的倒数第k个结点

将数组的奇数移到前面偶数到后面，即采用前面和后面往中间去遍历，如果满足条件则交换的算法。

关键是对于交换满足条件的判断，采用函数指针。

#include<iostream>
#include<string>
using namespace std;

bool Isodd(int n){
	if(n%2 == 1)
		return true;
	else
		return false;
}

void reorder(int *numbers,int length,bool (*func)(int)){
	if(length == 0|| numbers == NULL)
		return;
	int beg =0,end = length-1;
	while(beg<end){
		while(beg<end && func(numbers[beg]))
			beg++;
		while(beg<end && !func(numbers[end]))
			end--;
		if(beg < end){
			int temp = numbers[beg];
			numbers[beg] = numbers[end];
			numbers[end] = temp;
		}
	}
}
int main(){
	int numbers[] = {2,4,8,1,3,9,6};
	reorder(numbers,7,Isodd);
	for(int i =0;i<7;i++)
		printf("%d",numbers[i]);
	system("PAUSE");
	return 0;
}

输出链表的倒数第k个结点。题目简单，先一个指针走k步，然后另一个指针和先前的指针一起走，等先前的指针指向末尾，则另一个指针达到倒数第k个点。

关键是寻找倒数k时的健壮性。

#include<iostream>
#include<string>
#include<stack>
using namespace std;
struct ListNode{
	int value;
	ListNode* next;
};
//增加元素
void AddToList(ListNode** pHead,int value){
	ListNode* pTemp = *pHead; 
	pTemp = (ListNode *)malloc(sizeof(ListNode));
	pTemp->value = value;
	pTemp->next = NULL;
	if(*pHead == NULL)
		*pHead = pTemp;
	else{
		ListNode* pNTemp = *pHead;
		while(pNTemp->next != NULL)
			pNTemp = pNTemp->next;
		pNTemp->next = pTemp;
	}
}
//求长度
int ListLen(ListNode* pHead){
	int n =0;
	while(pHead != NULL){
		pHead = pHead->next;
		n++;
	}
	return n;
}
//返回0则表示不存在
int getlastk(ListNode* pHead,int k){
	if(pHead == NULL || k == 0)
		return 0;
	int len = ListLen(pHead);
	ListNode *pbeg = pHead;
	ListNode *pend = NULL;
	for(int i =0;i<k-1;i++){
		if(pbeg->next != NULL)
			pbeg = pbeg->next;
		else
			return 0;
	}
	pend = pHead;
	while(pbeg->next != NULL){
		pbeg = pbeg->next;
		pend = pend->next;
	}
	return pend->value;
}

int main(){
	ListNode* pHead = NULL;
	AddToList(&pHead,1);
	AddToList(&pHead,2);
	AddToList(&pHead,3);
	AddToList(&pHead,4);
	AddToList(&pHead,5);
	AddToList(&pHead,6);
	int value;
	value = getlastk(pHead,2);
	printf("%d\n",value);
	value = getlastk(pHead,7);
	printf("%d\n",value);
	system("PAUSE");
	return 0;
}