poj 1011 Sticks

Thinking:

1. Sort the sticks from the longest to the shortest.

2. Among those small sticks, we start from the largest one Smax. The length of the complete stick  L should range from Smax to (Sum of sticks),and Sum%L == 0

AC code:

#include<iostream>#include<cstring>#include<cmath>#include<algorithm>using namespace std;bool cmp(const int a,const int b){    return a > b;}int stk[70];bool used[70];int per;// Lint n;bool check_validity(int remain,int n_stk,int now_stk)// remain: how long do we need to complete current stick{//n_stk: how many sticks should be assembled    //now_stk :the stick chosen last time    if(n_stk== 1)// if there is only one stick left to be complete, then it's perfect        return true;    if(remain == per)//start of a new stick    {        int k = 1;        while(used[k]) k++;// find the largest unused stick        used[k] = true;        if(check_validity(remain-stk[k],n_stk,k))//assemble            return true;        used[k] = false;        return false;    }    else if(remain == 0)//finished the assembling of a stick        return check_validity(per,n_stk-1,1);//start next one    else    {        for(int i = now_stk+1;i <= n;i++)        {            if(!used[i]&&(remain-stk[i] >=0))// choose unused ones and remain should be larger than the stk            {                if(!used[i-1]&&stk[i] == stk[i-1])continue;// **important  if the stk[j] failed and stk[j+1] == stk[j],it is unnecessary to try j+1                 used[i] = true;                if(check_validity(remain-stk[i],n_stk,i))                    return true;                used[i] = false;            }        }        return false;    }}int main(){    while(scanf("%d",&n)&&n)    {            for(int i = 1;i <= n;i++)                scanf("%d",&stk[i]);        sort(stk+1,stk+1+n,cmp);        int maxx = stk[1];        int sum(0);        bool flag =false;        for(int i = 1;i <= n;i++)            sum+=stk[i];        for(int i = maxx;i <= sum/2;i++)        {            memset(used,false,sizeof(used));            if(sum % i == 0)            {                per = i;                if(check_validity(i,sum/i,1))                {                    flag = true;                    printf("%d\n", i);                    break;                }            }        }        if(!flag)            printf("%d\n",sum);    }return 0;}