hdu 1034 (preprocess optimization, property of division to avoid if, decreasing order process)

IMO, version 1 better than version 2, version 2 better than version 3.

make some preprocess to make you code simple and efficient. Here divide the input by 2, so you don’t have to do dividsion on each loop.

version 1 is best

thanks to

http://www.cnblogs.com/kuangbin/archive/2012/06/03/2532690.html

[code]#include <cstdio>
#include <algorithm>

#define MAXSIZE 10000

int candies[MAXSIZE];

int main() {
    //freopen("input.txt","r",stdin);
    int n, cnt_whistle, i, tmp;
    while(scanf("%d",&n)!=EOF && n>0) {
        for(i=0;i<n;++i) { scanf("%d",&tmp); candies[i]=tmp>>1; }
        for(--n, cnt_whistle=1;;++cnt_whistle) {
            tmp=candies
;
            for(i=n;i>0;--i) {
                candies[i]=(candies[i-1]+candies[i]+1)>>1;
            }
            candies[0]=(tmp+candies[0]+1)>>1;
            for(i=1;i<=n && candies[i-1]==candies[i];++i) ;
            if(i-n==1) break;
        }
        printf("%d %d\n",cnt_whistle,candies[0]<<1);
    }
    return 0;
}

use division’s floor property (5/2=2) to avoid if sentences. in version 2 here

[code]t2=candies[i];
candies[i]=(t1+t2+1)>>1;
t1=t2;

if don’t divide input by 2, the code will be

[code]t2=candies[i]>>1;
candies[i]=t1+t2;
if(candies[i]%2) ++candies[i];
t1=t2;

how to avoid process the border conditions? version 2 better than version 3 on this aspect. version 1 accomplish this, thanks to

http://www.acmerblog.com/hdu-1034-candy-sharing-game-1285.html

version 2

[code]#include <cstdio>
#include <algorithm>

#define MAXSIZE 10000

int candies[MAXSIZE];

int main() {
    //freopen("input.txt","r",stdin);
    int n, cnt_whistle, i, t1,t2;
    while(scanf("%d",&n)!=EOF && n>0) {
        for(i=0;i<n;++i) { scanf("%d",&t1); candies[i]=t1>>1; }
        for(--n, cnt_whistle=1;;++cnt_whistle) {
            t1=candies
;
            for(i=0;i<=n;++i) {
                t2=candies[i];
                candies[i]=(t1+candies[i]+1)>>1;
                t1=t2;
            }
            for(i=1;i<=n && candies[i-1]==candies[i];++i) ;
            if(i-n==1) break;
        }
        printf("%d %d\n",cnt_whistle,candies[0]<<1);
    }
    return 0;
}

version 3

[code]#include <cstdio>
#include <algorithm>

#define MAXSIZE 10000

int candies[MAXSIZE];
int cand_temp[MAXSIZE];

int main() {
    //freopen("input.txt","r",stdin);
    int n, cnt_whistle, i, *p,*q;
    while(scanf("%d",&n)!=EOF && n>0) {
        for(i=0;i<n;++i) { scanf("%d",&t1); candies[i]=t1>>1; }
        p=candies, q=cand_temp;
        for(--n, cnt_whistle=1;;++cnt_whistle) {
            for(i=1;i<=n;++i) {
                q[i]=(p[i-1]+p[i]+1)>>1;
            }
            q[0]=(p
+p[0]+1)>>1;
            std::swap(p,q);
            for(i=1;i<=n && p[i-1]==p[i];++i) ;
            if(i-n==1) break;
        }
        printf("%d %d\n",cnt_whistle,p[0]<<1);
    }
    return 0;
}

p.s. when you use swap tricks (as in version 3), be careful with the check points, e.g. the initialization part, the conclusion part, especially the items are used by multiple times.

here is mistake I made, 1st, initilization error

position of

[code]cnt_whistle=1;

mistakely put it to declaration part rather than just befor the for loop;

2nd, the third parameter of printf

mistakely wirite

[code]printf("%d %d\n",cnt_whistle,candies[0]<<1);

which should be

[code]printf("%d %d\n",cnt_whistle,p[0]<<1);