HDU 4310 Hero (贪心)

题意：给定你有 n 个敌人，你的伤害是 1，给出每个敌人的伤害，和敌人的血量，每一回合你可以攻击一个敌人，并且所有敌人都会攻击你，除非它已经死了，问你最少要多少要消耗多少血量。

析：一个很明显的贪心问题，按照 攻击 / 血量进行排序，然后一个一个的消灭就好了。

代码如下：

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <cstdio>
#include <string>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <cstring>
#include <set>
#include <queue>
#include <algorithm>
#include <vector>
#include <map>
#include <cctype>
#include <cmath>
#include <stack>
#include <sstream>
#include <list>
#include <assert.h>
#include <bitset>
#include <numeric>
#define debug() puts("++++")
#define gcd(a, b) __gcd(a, b)
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define fi first
#define se second
#define pb push_back
#define sqr(x) ((x)*(x))
#define ms(a,b) memset(a, b, sizeof a)
#define sz size()
#define be begin()
#define ed end()
#define pu push_up
#define pd push_down
#define cl clear()
#define lowbit(x) -x&x
//#define all 1,n,1
#define FOR(i,n,x)  for(int i = (x); i < (n); ++i)
#define freopenr freopen("in.in", "r", stdin)
#define freopenw freopen("out.out", "w", stdout)
using namespace std;
 
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int, int> P;
const int INF = 0x3f3f3f3f;
const LL LNF = 1e17;
const double inf = 1e20;
const double PI = acos(-1.0);
const double eps = 1e-10;
const int maxn = 20 + 5;
const int maxm = 700 + 10;
const LL mod = 1000000007;
const int dr[] = {-1, 1, 0, 0, 1, 1, -1, -1};
const int dc[] = {0, 0, 1, -1, 1, -1, 1, -1};
const char *de[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};
int n, m;
const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
inline bool is_in(int r, int c) {
  return r >= 0 && r < n && c >= 0 && c < m;
}
inline int readInt(){ int x;  scanf("%d", &x);  return x; }
 
struct Node{
  int dps, hp;
  bool operator < (const Node &p) const{
    return p.dps * hp < p.hp * dps;
  }
};
 
Node a[maxn];
 
int main(){
  while(scanf("%d", &n) == 1){
    for(int i = 0; i < n; ++i)
      scanf("%d %d", &a[i].dps, &a[i].hp);
    sort(a, a + n);
    LL ans = 0, cnt = 0;
    for(int i = 0; i < n; ++i){
      cnt += a[i].hp;
      ans += a[i].dps * cnt;
    }
    printf("%I64d\n", ans);
  }
  return 0;
}