UVA-307 sticks (dfs+ pruning)

The main topic: with n length may not be equal to match the maximum number of sticks.

Title Analysis: Enumerate the lengths of all possible equal-length sticks, match each root by DFS, and prune them in the process. The length of the stick is sorted from large to small, that is to say, it is always preferred to match each long stick. The pruning scheme is as follows: 1. If the i-1 stick is not used in the matching of the current scheme and length[i]==length[i-1], then the root of the first stick is also impossible to use; 2. If the successful CNT root is matched to a long stick, and the first cnt+1 root match is unsuccessful, then pruning; 3. If the match is in the cnt+ 1 sticks, the longest stick stick will be the first to be selected, if at this time cnt+1 root and other long stick match failure, then the first cnt+1 root and other long sticks do not need to continue matching, return to the first CNT root and other long stick matching can, because the match with stick in this matching the range of the optional stick is larger than the future , this is not matched, later more matching is not, to re-match the first CNT stick, to produce a new longest stick stick ', and then try to match the cnt+1 root and other long sticks.

The above three is indispensable!!!

The code is as follows:

# include<iostream># include<cstdio># include<vector># include<cstring># include< Algorithm>using namespace Std;int w[100],n,vis[100];bool mycomp (const int &a,const int &b) {return a>b;}    BOOL Dfs (int cur,int g,int id,int cnt,int sum) {if (g*cnt==sum) return true;        for (int i=id;i<n;++i) {if (vis[i]) continue;        if (I&&!vis[i-1]&&w[i-1]==w[i])///pruning 1 continue;            if (cur+w[i]==g) {vis[i]=1;            if (Dfs (0,g,0,cnt+1,sum)) return true;            vis[i]=0;            return false;///Pruning 2} else if (cur+w[i]<g) {vis[i]=1;            if (Dfs (cur+w[i],g,i+1,cnt,sum)) return true;            vis[i]=0; if (cur==0) return false;///pruning 3}} return false;    int main () {int sum;        while (~SCANF ("%d", &n) &&n) {sum=0; for (int i=0;i<n;++i) {scanf ("%d ", w+i);        Sum+=w[i];        } sort (W,w+n,mycomp);        int flag=0;                for (int g=w[0];g<=sum/2;++g) {if (sum%g==0) {memset (vis,0,sizeof (VIS));                    if (Dfs (0,g,0,1,sum)) {flag=1;                    printf ("%d\n", g);                Break    }}} if (!flag) printf ("%d\n", sum); } return 0;}

　　

UVA-307 sticks (dfs+ pruning)