POJ 1837 Balance
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Balance
Time Limit: 1000MS Memory Limit: 30000KTotal Submissions: 11113 Accepted: 6903
Description
Gigel has a strange "balance" and he wants to poise it. Actually, the device is different from any other ordinary balance.
It orders two arms of negligible weight and each arm's length is 15. Some hooks are attached to these arms and Gigel wants to hang up some weights from his collection of G weights (1 <= G <= 20) knowing that these weights have distinct values in the range 1..25. Gigel may droop any weight of any hook but he is forced to use all the weights.
Finally, Gigel managed to balance the device using the experience he gained at the National Olympiad in Informatics. Now he would like to know in how many ways the device can be balanced.
Knowing the repartition of the hooks and the set of the weights write a program that calculates the number of possibilities to balance the device.
It is guaranteed that will exist at least one solution for each test case at the evaluation.
It orders two arms of negligible weight and each arm's length is 15. Some hooks are attached to these arms and Gigel wants to hang up some weights from his collection of G weights (1 <= G <= 20) knowing that these weights have distinct values in the range 1..25. Gigel may droop any weight of any hook but he is forced to use all the weights.
Finally, Gigel managed to balance the device using the experience he gained at the National Olympiad in Informatics. Now he would like to know in how many ways the device can be balanced.
Knowing the repartition of the hooks and the set of the weights write a program that calculates the number of possibilities to balance the device.
It is guaranteed that will exist at least one solution for each test case at the evaluation.
Input
The input has the following structure:
• the first line contains the number C (2 <= C <= 20) and the number G (2 <= G <= 20);
• the next line contains C integer numbers (these numbers are also distinct and sorted in ascending order) in the range -15..15 representing the repartition of the hooks; each number represents the position relative to the center of the balance on the X axis (when no weights are attached the device is balanced and lined up to the X axis; the absolute value of the distances represents the distance between the hook and the balance center and the sign of the numbers determines the arm of the balance to which the hook is attached: '-' for the left arm and '+' for the right arm);
• on the next line there are G natural, distinct and sorted in ascending order numbers in the range 1..25 representing the weights' values.
• the first line contains the number C (2 <= C <= 20) and the number G (2 <= G <= 20);
• the next line contains C integer numbers (these numbers are also distinct and sorted in ascending order) in the range -15..15 representing the repartition of the hooks; each number represents the position relative to the center of the balance on the X axis (when no weights are attached the device is balanced and lined up to the X axis; the absolute value of the distances represents the distance between the hook and the balance center and the sign of the numbers determines the arm of the balance to which the hook is attached: '-' for the left arm and '+' for the right arm);
• on the next line there are G natural, distinct and sorted in ascending order numbers in the range 1..25 representing the weights' values.
Output
The output contains the number M representing the number of possibilities to poise the balance.
Sample Input
2 4-2 3 3 4 5 8
Sample Output
2
题意:
有C个位置,G个砝码,用所有的砝码将天平调平衡,求有多少种方案。
题解:
从砝码入手,考虑每个砝码放的位置,用平衡度来判断天平平衡,根据杠杆原理,左右两边的臂长*砝码质量的和相等,左边位置为负值,于是平衡度为0时平衡,还有就是平衡度会出现负值,最大为-7500,只要把DP数组向右移7500
代码:
#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>using namespace std;int c[25];int g[25];int dp[25][15100];int main(){ int n,m; while(~scanf("%d%d",&n,&m)) { for(int i=1;i<=n;i++) { scanf("%d",&c[i]); } for(int i=1;i<=m;i++) scanf("%d",&g[i]); memset(dp,0,sizeof(dp)); dp[0][7500]=1; for(int i=1;i<=m;i++) { for(int j=-7500;j<=7500;j++) { if(dp[i-1][j+7500]) { for(int k=1;k<=n;k++) { dp[i][j+c[k]*g[i]+7500]+=dp[i-1][j+7500]; } } } } printf("%d\n",dp[m][7500]); } return 0;}
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