贪心 Codeforces Round #297 (Div. 2) C. Ilya and Sticks

 

题目传送门

 1 /*  2  题意：给n个棍子，组成的矩形面积和最大，每根棍子可以-1  3  贪心：排序后，相邻的进行比较，若可以读入x[p++]，然后两两相乘相加就可以了  4 */  5 #include <cstdio>  6 #include <algorithm>  7 #include <cstring>  8 #include <cmath>  9 using namespace std; 10 11 typedef long long ll; 12 13 const int MAXN = 1e5 + 10; 14 const int INF = 0x3f3f3f3f; 15 int a[MAXN]; 16 ll x[MAXN]; 17 int vis[MAXN]; 18 19 int main(void) //Codeforces Round #297 (Div. 2) C. Ilya and Sticks 20 { 21 int n; 22 while (scanf ("%d", &n) == 1) 23  { 24 memset (x, 0, sizeof (x)); 25 for (int i=1; i<=n; ++i) scanf ("%d", &a[i]); 26 sort (a+1, a+1+n); 27 int p = 0; 28 for (int i=n; i>=2; --i) 29  { 30 if (a[i] == a[i-1]) {x[p++] = a[i]; i--;} 31 else if (a[i] == a[i-1] + 1) {x[p++] = a[i-1]; i--;} 32  } 33 34 if (p < 2) puts ("0"); 35 else 36  { 37 ll sum = 0; x[p] = 1; 38 for (int i=0; i<p; i+=2) 39  { 40 sum += (x[i] * x[i+1]); 41  } 42 if (p & 1) sum -= x[p-1]; 43 printf ("%I64d\n", sum); 44  } 45  } 46 47 return 0; 48 } 49 50 51 /* 52 4 53 2 4 4 2 54 4 55 2 2 3 5 56 4 57 100003 100004 100005 100006 58 5 59 1 1 1 1 1 60 10 61 3 3 5 4 2 2 5 6 7 5 62 */