Numbers Appearing Once

最新推荐文章于 2025-01-13 15:16:10 发布

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本文介绍了一种算法，用于在一个所有数都出现三次的数组中找到只出现一次的数。通过位运算，该算法有效地解决了这个问题。

Problem: In an array, all numbers appear three times except one which only appears only once. Please find the unique number.

参考：http://codercareer.blogspot.com/2013/12/no-50-numbers-appearing-once.html

/* Copyleft: Ming Lin <minggr@gmail.com> */

#include <stdio.h>

void calculate_one(int *count, int data)
{
	int i = 0;

	while (data) {
		if (data & 1)
			count[i]++;
		i++;
		data = data >> 1;	
	}
}

int find_unique(int data[], int n)
{
	int count[32];
	int i;	
	int r = 0;

	for (i = 0; i < 32; i++)
		count[i] = 0;

	for (i = 0; i < n; i++)
		calculate_one(count, data[i]);

	for (i = 0; i < 32; i++) {
		if (count[i] % 3)
			r |= (1 << i);
	}

	return r;
}

int main()
{
	int data[] = {9, 100, 5, 5, 9, 9, 80, 5, 80, 80};
	int n = 10;

	printf("%d\n", find_unique(data, n));
	return 0;
}