[USACO09MAR]Sand Castle

嘟嘟嘟

太水了，大佬们就绕道吧……

就是m, b数组分别排个序，然后更改对应位置的m[i]和b[i]，就行了。

因为如果m[i]不改为b[i]而是b[i + 1]的话，那么必定要将m[j] (j > i)改为b[i],而这一定比m[i]改为b[i]更劣。

 #include<cstdio>
 #include<iostream>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #include<cstdlib>
 #include<cctype>
 #include<vector>
 #include<stack>
 #include<queue>
 using namespace std;
 #define enter puts("")
 #define space putchar(' ')
 #define Mem(a) memset(a, 0, sizeof(a))
 typedef long long ll;
 typedef double db;
 const int INF = 0x3f3f3f3f;
 const db eps = 1e-;
 const int maxn = 2.5e4 + ;;
 inline ll read()
 {
     ll ans = ;
     char ch = getchar(), last = ' ';
     while(!isdigit(ch)) {last = ch; ch = getchar();}
     while(isdigit(ch)) {ans = ans *  + ch - ''; ch = getchar();}
     if(last == '-') ans = -ans;
     return ans;
 }
 inline void write(ll x)
 {
     if(x < ) x = -x, putchar('-');
     if(x >= ) write(x / );
     putchar(x %  + '');
 }

 int n, x, y;
 int m[maxn], b[maxn];
 ll ans = ;

 int main()
 {
     n = read(); x = read(); y = read();
     for(int i = ; i <= n; ++i) m[i] = read(), b[i] = read();
     sort(m + , m + n + ); sort(b + , b + n + );
     for(int i = ; i <= n; ++i) ans += (m[i] - b[i]) * (m[i] > b[i] ? y : -x);
     write(ans); enter;
     return ;
 }