poj 1579 Function Run Fun(记忆化搜索+dp)

题目链接：http://poj.org/problem?id=1579

思路分析：题目给出递归公式，使用动态规划的记忆搜索即可解决。

代码如下: 

#include <stdio.h>
#include <string.h>

const int MAX_N = 20 + 5;
int dp[MAX_N][MAX_N][MAX_N];

int w( int a, int b, int c )
{
    if ( dp[a][b][c] != -1 )
        return dp[a][b][c];

    if ( a <= 0 || b <= 0 || c <= 0 )
        return dp[a][b][c] = 1;
    else
    if ( a < b && b < c )
        return dp[a][b][c] = w(a, b, c-1) + w(a, b-1, c-1) - w(a, b-1, c);
    else
        return dp[a][b][c] = w( a-1, b, c) + w( a-1, b-1, c) + 
               w( a-1, b, c-1 ) - w( a-1, b-1, c-1);
}

int main()
{
    int a, b, c;
    int ans = 0;

    while ( scanf( "%d %d %d", &a, &b, &c ) != EOF )
    {
        if ( a == -1 && b == -1 && c == -1 )
            break;

        memset( dp, -1, sizeof(dp) );
        if ( a <= 0 || b <= 0 || c <= 0 )
            ans = 1;
        else
        if ( a > 20 || b >20 || c > 20 )
            ans = w(20, 20, 20);
        else
            ans = w(a, b, c);

        printf( "w(%d, %d, %d) = %d
", a, b, c, ans );
    }

    return 0;
}