Chap5: question: 29 - 31

29. 数组中出现次数超过一半的数字.

方法a. 排序取中       O(nlogn).

方法b. partition 函数分割找中位数         
>=O(n).

方法c. 设计数变量，扫描一遍。     O(n).

#include <stdio.h>

bool Invalid_Input = false;

int getNumber(int data[], int length){

    Invalid_Input = false;

    if(!data || length < 1) { Invalid_Input = true; return 0; }

    int count = 1, value = data[0];

    for(int i = 1; i < length; ++i)

    {

        if(count == 0){

            value = data[i];

            count = 0;

        }else if(data[i] == value){

            ++count;

        }else

            --count;

    }

    return value;

}

int main(){

    int numbers[] = {2, 2, 2, 2, 6, 6, 6, 6, 6};

    int value = getNumber(numbers, sizeof(numbers) / 4);

    if(value && !Invalid_Input)

        printf("%d\n", value);

    return 0;

}