Hamming Distance HDU - 4712 （随机）

最新推荐文章于 2019-09-27 19:59:55 发布

转载最新推荐文章于 2019-09-27 19:59:55 发布 · 204 阅读

文章标签：

#随机算法

技巧同时被 3 个专栏收录

16 篇文章

订阅专栏

优化

2 篇文章

订阅专栏

随机算法

1 篇文章

订阅专栏

本文介绍了一种计算不同十六进制编码的二进制字符串间最小汉明距离的方法。通过随机选择字符串对并计算它们之间的汉明距离来找到最小值。采用优化后的算法提高了计算效率。

Hamming Distance

HDU - 4712

(From wikipedia) For binary strings a and b the Hamming distance is equal to the number of ones in a XOR b. For calculating Hamming distance between two strings a and b, they must have equal length.
Now given N different binary strings, please calculate the minimum Hamming distance between every pair of strings.

Input

The first line of the input is an integer T, the number of test cases.(0<T<=20) Then T test case followed. The first line of each test case is an integer N (2<=N<=100000), the number of different binary strings. Then N lines followed, each of the next N line is a string consist of five characters. Each character is '0'-'9' or 'A'-'F', it represents the hexadecimal code of the binary string. For example, the hexadecimal code "12345" represents binary string "00010010001101000101".

Output

For each test case, output the minimum Hamming distance between every pair of strings.

Sample Input

Sample Output

6
7

https://blog.youkuaiyun.com/HackerTom/article/details/73189121

#include <algorithm>
#include <cstring>
#include <cstdio>
#include <ctime>
using namespace std;
const int N = 1e5 + 7;
int a[N];

int dis(int x, int y) {
	x = a[x] ^ a[y];
	y = 0;
	for (int i = 0; i < 20; ++i) {
		y += ((x >> i) & 1);
	}
	return y;
} 

int main() {
	
	srand((unsigned)time(NULL)); //把时间作为随机函数的种子 
	int t;
	scanf ("%d", &t);
	while (t--) {
		int n;
		scanf ("%d", &n);
		for (int i = 1; i <= n; ++i) {
			scanf ("%x", a+i); //%x读入一个16进制 
		}
		int ans = 0x3f3f3f3f;
		for (int i = 1, x, y; i <= 500000; ++i) { //随机选500000次 
			x = rand() % n + 1;
			y = rand() % n + 1;
			if (x == y) continue;
			ans = min(ans, dis(x, y));
		} 
		printf ("%d\n", ans);
	}
	
	return 0;
}

优化：

#include <algorithm>
#include <cstring>
#include <cstdio>
#include <ctime>
using namespace std;
const int N = 1e5 + 7;
int a[N];

int dis(int x, int y) {
	x = a[x] ^ a[y];
	y = 0;
	while (x) y += x&1, x >>= 1;
	return y;
} 

int main() {
	
	srand((unsigned)time(NULL)); //把时间作为随机函数的种子 
	int t;
	scanf ("%d", &t);
	while (t--) {
		int n;
		scanf ("%d", &n);
		for (int i = 1; i <= n; ++i) {
			scanf ("%x", a+i); //%x读入一个16进制 
		}
		int ans = 0x3f3f3f3f;
		int m = n * (rand()%100+100);
		m = min(m, 200000);
		for (int i = 1, x, y; i <= m; ++i) { //随机选m次 
			x = rand() % n + 1;
			y = rand() % n + 1;
			if (x == y) continue;
			ans = min(ans, dis(x, y));
		} 
		printf ("%d\n", ans);
	}
	
	return 0;
}