题目大意:有k个数组,每个数组选取一个数,组成k^k个数。在这k^k个数中选择最小的前k个数
解题思路:
1、如果只有k个数组,那么最后得到的最小的前k个数应该可以由前两个数组得到的最小k个数与第三个数组
按规则运算后得到。
2、如果每个数组只有3个数.那么前两个数组(a:(a0,a1,a2) b:(b0,b1,b2,a与b数组都已经有序)运算后有的结果矩阵如下:
a0+b0,a0+b1,a0+b2
a1+b0,a1+b1,a1+b2
a2+b0,a2+b1,a2+b2
在这个矩阵中,a0+b0肯定是最小的。如果一个队列里只维持3个最小数,那么下一个产生最小数的位置是
a0+b1.分析如下:
由a1+b1>a1+b0可知,a1+b1及其后面的不可能产生下一个最小数.依照此逻辑可知下一个可能产生最小数的位置
是a0+b1
3、在以下的这种解法中,他并没有算出k^k个结果,它其实质算了n+n个可能产生最小数的结果而已
。
Problem K
K Smallest Sums
You‘re given k arrays, each array has k integers. There are kk ways to pick exactly one element in each array and calculate the sum of the integers. Your task is to find the k smallest sums among them.
Input
There will be several test cases. The first line of each case contains an integer k (2<=k<=750). Each of the following k lines contains k positive integers in each array. Each of these integers does not exceed 1,000,000. The input is terminated by end-of-file (EOF). The size of input file does not exceed 5MB.
Output
For each test case, print the k smallest sums, in ascending order.
Sample Input
3 1 8 5 9 2 5 10 7 6 2 1 1 1 2
Output for the Sample Input
9 10 12 2 2
Rujia Liu‘s Present 3: A Data Structure Contest Celebrating the 100th Anniversary of Tsinghua University
Special Thanks: Yiming Li
Note: Please make sure to test your program with the gift I/O files before submitting!
代码如下:
/* * UVA_11997.cpp * * Created on: 2014年12月30日 * Author: Administrator */ #include <iostream> #include <cstdio> #include <queue> #include <algorithm> using namespace std; const int maxn = 758; int A[maxn][maxn]; struct Item{ int s,b; Item(int s,int b):s(s),b(b){ } bool operator < (const Item& b) const{ return s > b.s; } }; void merge(int* A,int* B,int* C,int n){ priority_queue<Item> q; int i; for(i = 0 ; i < n ; ++i){ q.push(Item(A[i] + B[0],0)); } for(i = 0 ; i < n ; ++i){ Item item = q.top(); q.pop(); C[i] = item.s; int b = item.b; if(b+1 < n){ q.push(Item(item.s - B[b] + B[b+1],b+1)); } } } int main(){ int n; while(scanf("%d",&n) == 1){ int i; int j; for(i = 0 ; i < n ; ++i){ for(j = 0 ; j < n ; ++j){ scanf("%d",&A[i][j]); } sort(A[i],A[i]+n); } for(i = 1 ; i < n ; ++i){ merge(A[0],A[i],A[0],n); } printf("%d",A[0][0]); for(i = 1 ; i < n ; ++i){ printf(" %d",A[0][i]); } printf("\n"); } return 0; }