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poj 1147 Binary codes
Time Limit: 1000MS | Memory Limit: 65536K | |
Total Submissions: 5647 | Accepted: 2201 |
Description
Consider a binary string (b1…bN) with N binary digits. Given such a string, the matrix of Figure 1 is formed from the rotated versions of the string.
b1 | b2 | … | bN?1 | bN |
b2 | b3 | … | bN | b1 |
… | ||||
bN?1 | bN | … | bN?3 | bN?2 |
bN | b1 | … | bN?2 | bN?1 |
Figure 1. The rotated matrix
Then rows of the matrix are sorted in alphabetical order, where ‘0’ is before ‘1’. You are to write a program which, given the last column of the sorted matrix, finds the first row of the sorted matrix.
As an example, consider the string (00110). The sorted matrix is
0 | 0 | 0 | 1 | 1 |
0 | 0 | 1 | 1 | 0 |
0 | 1 | 1 | 0 | 0 |
1 | 0 | 0 | 0 | 1 |
1 | 1 | 0 | 0 | 0 |
and the corresponding last column is (1 0 0 1 0). Given this last column your program should determine the first row, which is (0 0 0 1 1).
Input
The first line contains one integer N ≤ 3000, the number of binary digits in the binary string. The second line contains N integers, the binary digits in the last column from top to bottom.
Output
The first line contains N integers: the binary digits in the first row from left to right.
Sample Input
5 1 0 0 1 0
Sample Output
0 0 0 1 1
对由0,1组成的n个数,照题中的旋转,最后根据每行的字典序排序,组成n*n的矩阵,给出矩阵的最后1列,求矩阵
的第首行。
给出最后一列可以求出第0列,因为是按字典序排的,所以第0列肯定0在前,1在后,而第0列为0的相对位置在最后
1列不变,因为第0列都为0,又是按字典序排的。第0列为1也一样。根据第0列和最后一列就可以将对应关系求出,
也就是next数组。
例如样例的
0 0 0 1 1
0 0 1 1 0
0 1 1 0 0
1 0 0 0 1
1 1 0 0 0
next[ ]={1,2,4,0,3}
第0行第0列为0,第0行的第1列下次旋转后为第0列的第0行,所以第0行第1列为第0列的第1行为0,第1列的第0行
为第2列的第1行,为第0列的第2行,所以第0行的第2列为第0列的第2行为0,通过推理发现为next数组中元素递推
代码:
#include <iostream> #include <cstdio> #include <algorithm> using namespace std; const int maxn=5000+100; int last[maxn]; int first[maxn]; int next[maxn]; int main() { int n; while(~scanf("%d",&n)) { for(int i=0;i<n;i++) { scanf("%d",&last[i]); first[i]=last[i]; } sort(first,first+n); int cur=0; int i; for(i=0;i<n;i++) { if(first[i]) break; while(last[cur]&&cur<n) cur++; next[i]=cur++; } cur=0; for(i=i;i<n;i++) { while(last[cur]==0&&cur<n) cur++; next[i]=cur++; } int k=0; for(int i=0;i<n-1;i++) { printf("%d ",first[k]); k=next[k]; } printf("%d\n",first[k]); } return 0; }
poj 1147 Binary codes