POJ1579 Function Run Fun

Function Run Fun

Time Limit: 1000ms

Memory Limit: 10000KB

This problem will be judged on PKU. Original ID: 1579
64-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. 

 

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

Pacific Northwest 1999

 

解题：一个寒假没写代码了啊。。。。。。。先找下感觉啊。。。

 

/*
@author: Lev
@date:
*/
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <cstdlib>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <climits>
#include <deque>
#include <sstream>
#include <fstream>
#include <bitset>
#include <iomanip>
#define LL long long
#define PI acos(-1)
using namespace std;
int dp[30][30][30];
int go(int a,int b,int c) {
    if(a <= 0 || b <= 0 || c <= 0) return 1;
    if(a > 20 || b > 20 || c > 20) return go(20,20,20);
    if(dp[a][b][c]) return dp[a][b][c];
    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);
    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);
    return dp[a][b][c];
}
int main() {
    memset(dp,0,sizeof(dp));
    int a,b,c;
    while(~scanf("%d %d %d",&a,&b,&c)) {
        if(a == -1 && b == -1 && c == -1) break;
        printf("w(%d, %d, %d) = %d\n",a,b,c,go(a,b,c));
    }
    return 0;
}