本文地址: http://blog.csdn.net/caroline_wendy
题目: 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.
1. 使用快速排序(QuickSort)的方法, 把中值(middle)和索引(index)匹配, 输出中值, 并检测是否符合要求.
2. 使用计数方法依次比较.
代码:
方法1:
/*
* main.cpp
*
* Created on: 2014.6.12
* Author: Spike
*/
/*eclipse cdt, gcc 4.8.1*/
#include <stdio.h>
#include <stdlib.h>
int RandomInRange(int min, int max)
{
int random = rand() % (max - min + 1) + min;
return random;
}
void Swap(int* num1, int* num2)
{
int temp = *num1;
*num1 = *num2;
*num2 = temp;
}
int Partition(int data[], int length, int start, int end)
{
if(data == NULL || length <= 0 || start < 0 || end >= length) {
return -1;
}
int index = RandomInRange(start, end);
Swap(&data[index], &data[end]);
int small = start - 1;
for(index = start; index < end; ++ index)
{
if(data[index] < data[end])
{
++ small;
if(small != index)
Swap(&data[index], &data[small]);
}
}
++ small;
Swap(&data[small], &data[end]);
return small;
}
bool CheckMoreThanHalf (int* numbers, int length, int number)
{
int times = 0;
for (int i=0; i<length; ++i) {
if (numbers[i] == number)
++times;
}
if (times*2 <= length) {
return false;
}
return true;
}
int MoreThanHalfNum(int* numbers, int length) {
if (numbers == NULL || length <= 0)
return 0;
int middle = length >> 1;
int start = 0;
int end = length-1;
int index = Partition(numbers, length, start, end);
while (index != middle) {
if (index > middle) { //前面部分的数字多
end = index-1;
index = Partition(numbers, length, start, end);
} else {
start = index+1;
index = Partition(numbers, length, index+1, start);
}
}
int result = numbers[middle];
if (!CheckMoreThanHalf(numbers, length, result))
return 0;
return result;
}
int main(void)
{
int str[] = {1, 2, 3, 4, 4, 4, 5, 4, 4};
int result = MoreThanHalfNum(str, 9);
printf("reuslt = %d\n", result);
return 0;
}
方法2:
/*
* main.cpp
*
* Created on: 2014.6.12
* Author: Spike
*/
/*eclipse cdt, gcc 4.8.1*/
#include <stdio.h>
#include <stdlib.h>
bool CheckMoreThanHalf (int* numbers, int length, int number) {
int times = 0;
for (int i=0; i<length; ++i) {
if (numbers[i] == number)
times++;
}
if (times*2 < length)
return false;
return true;
}
int MoreThanHalfNum (int* numbers, int length) {
if (numbers == NULL || length <= 0)
return 0;
int result = numbers[0];
int times = 1;
for (int i=0; i<length; ++i) {
if (times == 0) {
result = numbers[i];
times = 1;
}
if (numbers[i] == result) times++;
else times--;
}
if (!CheckMoreThanHalf(numbers, length, result))
return 0;
return result;
}
int main(void)
{
int str[] = {1, 2, 3, 2, 2, 2, 5, 2, 4};
int result = MoreThanHalfNum(str, 9);
printf("reuslt = %d\n", result);
return 0;
}
reuslt = 4
编程算法 - 数组中出现次数超过一半的数字 代码(C),布布扣,bubuko.com
原文地址：http://blog.csdn.net/caroline_wendy/article/details/35814815
