面试题29：数组中出现次数超过一半的数字

题目描述

数组中有一个数字出现的次数超过数组长度的一半，请找出这个数字。例如输入一个长度为9的数组{1,2,3,2,2,2,5,4,2}。由于数字2在数组中出现了5次，超过数组长度的一半，因此输出2。

题目分析

剑指Offer（纪念版）P163

代码实现

int MoreThanHalfNum_Solution2(int* numbers, int length)
{
if(CheckInvalidArray(numbers, length))
return 0;

int result = numbers[0];
int times = 1;
for(int i = 1; i < length; ++i)
{
if(times == 0)
{
result = numbers[i];
times = 1;
}
else if(numbers[i] == result)
times++;
else
times--;
}

if(!CheckMoreThanHalf(numbers, length, result))
result = 0;

return result;
}

bool g_bInputInvalid = false;

bool CheckInvalidArray(int* numbers, int length)
{
g_bInputInvalid = false;
if(numbers == NULL && length <= 0)
g_bInputInvalid = true;

return g_bInputInvalid;
}

bool CheckMoreThanHalf(int* numbers, int length, int number)
{
int times = 0;
for(int i = 0; i < length; ++i)
{
if(numbers[i] == number)
times++;
}

bool isMoreThanHalf = true;
if(times * 2 <= length)
{
g_bInputInvalid = true;
isMoreThanHalf = false;
}

return isMoreThanHalf;
}