POJ1579 Function Run Fun
Function Run Fun
Time Limit: 1000ms
Memory Limit: 10000KB
This problem will be judged on PKU. Original ID: 157964-bit integer IO format: %lld Java class name: Main
We all love recursion! Don't we?
Consider a three-parameter recursive function w(a, b, c):
if a <= 0 or b <= 0 or c <= 0, then w(a, b, c) returns:
1
if a > 20 or b > 20 or c > 20, then w(a, b, c) returns:
w(20, 20, 20)
if a < b and b < c, then w(a, b, c) returns:
w(a, b, c-1) + w(a, b-1, c-1) - w(a, b-1, c)
otherwise it returns:
w(a-1, b, c) + w(a-1, b-1, c) + w(a-1, b, c-1) - w(a-1, b-1, c-1)
This is an easy function to implement. The problem is, if implemented directly, for moderate values of a, b and c (for example, a = 15, b = 15, c = 15), the program takes hours to run because of the massive recursion.
Consider a three-parameter recursive function w(a, b, c):
if a <= 0 or b <= 0 or c <= 0, then w(a, b, c) returns:
1
if a > 20 or b > 20 or c > 20, then w(a, b, c) returns:
w(20, 20, 20)
if a < b and b < c, then w(a, b, c) returns:
w(a, b, c-1) + w(a, b-1, c-1) - w(a, b-1, c)
otherwise it returns:
w(a-1, b, c) + w(a-1, b-1, c) + w(a-1, b, c-1) - w(a-1, b-1, c-1)
This is an easy function to implement. The problem is, if implemented directly, for moderate values of a, b and c (for example, a = 15, b = 15, c = 15), the program takes hours to run because of the massive recursion.
Input
The input for your program will be a series of integer triples, one per line, until the end-of-file flag of -1 -1 -1. Using the above technique, you are to calculate w(a, b, c) efficiently and print the result.
Output
Print the value for w(a,b,c) for each triple.
Sample Input
1 1 1 2 2 2 10 4 6 50 50 50 -1 7 18 -1 -1 -1
Sample Output
w(1, 1, 1) = 2 w(2, 2, 2) = 4 w(10, 4, 6) = 523 w(50, 50, 50) = 1048576 w(-1, 7, 18) = 1
Source
解题:一个寒假没写代码了啊。。。。。。。先找下感觉啊。。。
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 /* 2 @author: Lev 3 @date: 4 */ 5 #include <iostream> 6 #include <cstdio> 7 #include <cmath> 8 #include <cstring> 9 #include <string> 10 #include <cstdlib> 11 #include <algorithm> 12 #include <map> 13 #include <set> 14 #include <queue> 15 #include <climits> 16 #include <deque> 17 #include <sstream> 18 #include <fstream> 19 #include <bitset> 20 #include <iomanip> 21 #define LL long long 22 #define PI acos(-1) 23 using namespace std; 24 int dp[30][30][30]; 25 int go(int a,int b,int c) { 26 if(a <= 0 || b <= 0 || c <= 0) return 1; 27 if(a > 20 || b > 20 || c > 20) return go(20,20,20); 28 if(dp[a][b][c]) return dp[a][b][c]; 29 if(a < b && b < c) dp[a][b][c] = go(a,b,c-1)+go(a,b-1,c-1)-go(a,b-1,c); 30 else dp[a][b][c] = go(a-1, b, c) + go(a-1, b-1, c) + go(a-1, b, c-1) - go(a-1, b-1, c-1); 31 return dp[a][b][c]; 32 } 33 int main() { 34 memset(dp,0,sizeof(dp)); 35 int a,b,c; 36 while(~scanf("%d %d %d",&a,&b,&c)) { 37 if(a == -1 && b == -1 && c == -1) break; 38 printf("w(%d, %d, %d) = %d\n",a,b,c,go(a,b,c)); 39 } 40 return 0; 41 }
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