劍指offer 面試題29 尋找數組中出現次數超一半的數字

#include <iostream>
#include <time.h> //use time(NULL) in line8
#include <stdlib.h> //use srand() in line8
using namespace std;
//*****************************************************
//used by partition,get rand number in [start,end]
int RandomInRange(int start,int end){
	srand(time(NULL));
	return start+rand()%(end-start+1);
}
//used by partition,swap a and b
void swap(int *a,int *b){
	int tmp=*a;
	*a=*b;
	*b=tmp;
}
//famous function partition!
int partition(int *number,int length,int start,int end){
	//!!!!!!!!!!!!!!to be handle:how to use exception
	//if(number==NULL||length<=0||start<0||end>length-1)
		//throw new std::exception("Invalid Input.");
	int index=RandomInRange(start,end);
	swap(&number[end],&number[index]);
	int smallnext=start;
	for(int i=start;i<end;++i){
		if(number[i]<number[end] ){
			if(i!=smallnext)
				swap(&number[i],&number[smallnext]);
			++smallnext;
		}
	}
	swap(&number[smallnext],&number[end]);
	return smallnext;
}
//******************************************************

//solution 1:using partition and narrow to length/2
int MoreThanHalf(int *number,int length){
	if(number==NULL||length<=0)
		return 0;
	//get index==length/2 by using partition
	int start=0,end=length-1;
	int index=partition(number,length,start,end);
	while(index!=(length>>1)){
		if(index<(length>>1)){
			start=index+1;
			index=partition(number,length,start,end);
		}
		else{
			end=index-1;
			index=partition(number,length,start,end);
		}			
	}
	//check if result really appear more than half
	int count=0;
	for(int i=0;i<length;++i){
		if(number[i]==number[index])
			count++;
	}
	if(count*2<=length)
		return 0;
	//return result
	return number[index];
}

//solution2:get a number and count(not change the initial array)
int MoreThanHalf2(int *number,int length){
	if(number==NULL||length<=0)
		return 0;
	int result=*number;
	int count=1;
	for(int i=1;i<length;++i){
		if(count==0){
			result=number[i];
			count=1;
		}	
		else if(number[i]==result)
				++count;
			else
				--count;
	}
	//check if result really appear more than half
	int count2=0;
	for(int i=0;i<length;++i){
		if(number[i]==result)
			count2++;
	}
	if(count2*2<=length)
		return 0;
	return result;
}
int main(){
	int array[11]={5,2,4,2,5,2,5,2,2,3,2};
	cout<<MoreThanHalf(array,sizeof(array)/sizeof(array[0]));
	cout<<MoreThanHalf2(array,sizeof(array)/sizeof(array[0]));
}