Question

I am trying to solve the SPOJ problem “Cricket Tournament“. I wrote the code in python and also in c. In python it takes about 2 seconds for input 0.0 0/0 300. But in C it runs forever. Code in C is running for some smaller test cases like 19.5 0/0 1

Code in C

#include<stdio.h>
float ans[10][120][300]={0};
float recursion(int balls, int reqRuns, int wickets);
int readScore(void);

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        memset(ans,0,sizeof(ans));
        float overs;
        int myruns,wickets,target;
        scanf("%f",&overs);
        myruns=readScore();
        scanf("%d",&wickets);
        //printf("%d %d\n",myruns,wickets );
        scanf("%d",&target);
        //printf("%d %d %d\n",myruns,wickets,target);
        if(myruns>=target)
        {
            printf("%s\n","100.00");
            continue;
        }
        else if(wickets>=10)
        {
            printf("%s\n", "0.00");
            continue;
        }
        printf("overs = %f\n", overs);
        int ov = (int) overs;
        int ball = (int)(overs*10)%10;
        int totballs = 6*ov+ball;
        //printf("%d %d\n",ov,ball );
        //printf("%d %d %d\n",totballs, target- myruns,wickets );
        float finalAns = recursion(totballs,target-myruns, wickets)*100;
        printf("%.2f\n",finalAns);

    }
    return 0;
}

int readScore()
{
    char ch;
    int ans2=0;
    ch = getchar();
    //ch = getchar();
    //ans = ans*10 + ch-'0';
    //printf("sadasdas %d\n",ch );
    while(ch!='/')
    {
        ch=getchar();
        //printf(" ch = %d\n", ch-'0');
        if(ch!='/')
        ans2 = ans2*10 + ch-'0';

    }
    //printf("%d\n",ans );
    return ans2;
}

float recursion(int balls, int reqRuns, int wickets)
{
    if (reqRuns<=0)
        return 1;
    if (balls==120||wickets==10)
        return 0;
    if(ans[wickets][balls][reqRuns]!=0)
        return ans[wickets][balls][reqRuns];

    ans[wickets][balls][reqRuns] = (recursion(balls+1, reqRuns,wickets)+recursion(balls+1, reqRuns-1,wickets)+
    recursion(balls+1, reqRuns-2,wickets)+recursion(balls+1, reqRuns-3,wickets)+
    recursion(balls+1, reqRuns-4,wickets)+recursion(balls+1, reqRuns-5,wickets)+
    recursion(balls+1, reqRuns-6,wickets)+recursion(balls+1, reqRuns,wickets+1)+
    2*recursion(balls, reqRuns-1,wickets))/10;
    return ans[wickets][balls][reqRuns];
}

Code in Python

from __future__ import division

saved = {}
t = input()

def func(f):
    if f in saved:    return saved[f]
    x,y,z,n = f 
    if z >= n:    return 1
    if x == 120:    return 0 
    if y == 10:    return 0

    saved[f] = (func((x+1,y+1,z,n)) + func((x+1, y,z,n)) + func((x+1,y,z+1,n)) + func((x+1, y, z+2,n)) + func((x+1, y, z+3,n)) + func((x+1, y, z+4,n)) + func((x+1, y, z+5,n))+ func((x+1, y, z+6,n))+ func((x,y,z+1,n)) + func((x,y,z+1,n))) / 10
    return saved[f]

def converter(f):
    v = f.index('.')
    x,y = int(f[:v]), int(f[-1])
    return x*6+(y)

for i in range(t):
    x,y,z = raw_input().split()
    v = y.index('/')
    q = int(y[:v])
    x,y,z = converter(x), int(y[(v+1):]), int(z)
    print  '%.2f' % (100 * func((x,y,q,z)))

Answer 1

Your problem is that a lot of the results of the recursion are 0, so

if(ans[wickets][balls][reqRuns]!=0)
    return ans[wickets][balls][reqRuns];

fails to return the cached result in many cases, hence you’re recomputing many many results, while the check f in saved in Python prevents recomputation of the same values.

I changed your C code to set the initial entries of ans to contain negative numbers (if you know the floating point representation of your platform to be IEEE754, simply changing to memset(ans, 0x80, sizeof ans); will do), and replaced the condition with

if (ans[wickets][balls][reqRuns] >= 0)

and got the result immediately:

$ time ./a.out  < spoj_inp.txt 
overs = 0.000000
18.03

real    0m0.023s
user    0m0.020s
sys     0m0.002s