uva 10720

Havel-Hakimi定理

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>const int maxn = 10010;using namespace std;int deg[maxn];bool Cmp(int x,int y){ return x > y;}bool Havel_Hakimi(int n){    for(int i=0; i<=n-1; ++i){        sort(deg+i,deg+n,Cmp);        if(i+deg[i] >= n) return false;        if(!deg[i])  return true;//剪枝        for(int j=i+1; j<=i+deg[i]; ++j){             --deg[j];             if(deg[j] < 0) return false;        }    }    if(deg[n-1] != 0) return false;    return true;}int main(){    int n;    while(~scanf("%d",&n) && n){         bool flag = true;         int sum = 0;         for(int i= 0; i < n; ++i){              scanf("%d",°[i]);              sum += deg[i];              if(deg[i] > n-1) flag = false;         }         if(sum % 2 != 0) flag = false;         if(flag&&Havel_Hakimi(n))              printf("Possible\n");         else printf("Not possible\n");    }    return 0;}