USACO 1.3 Mixing Milk (快排+贪心)

#include <stdio.h>
#define DEBUG 0
#define TESTCASES 9

#define MAX_FARMERS 5000
int milkNeeded;
int numOfFarmers;
typedef struct Farmer{
int price;
int milk;
}Farmer;
Farmer farmers[MAX_FARMERS + 1];

void sortFarmersAccordingToPrice(int first, int last){
while (first < last){
Farmer pivotFarmer = farmers[first];
int pivotPrice = farmers[first].price;
int left = first;
int right = last;
while (left < right){
while (left < right && farmers[right].price >= pivotPrice)
right--;
farmers[left] = farmers[right];
while (left < right && farmers[left].price <= pivotPrice)
left++;
farmers[right] = farmers[left];
}
farmers[left] = pivotFarmer;
int pivot = left;
sortFarmersAccordingToPrice(first, pivot);
first = pivot + 1;
}
}
int mix(){
int minPrice = 0;
int milkMixed = 0;
int farmer;
for (farmer = 1; farmer <= numOfFarmers; farmer++){
if (milkMixed  + farmers[farmer].milk >= milkNeeded){
minPrice += farmers[farmer].price * (milkNeeded - milkMixed);
break;
} else {
milkMixed += farmers[farmer].milk;
minPrice += farmers[farmer].price * farmers[farmer].milk;
}
}
return minPrice;
}

int main(){
#if DEBUG
int testCase;
for (testCase = 1; testCase <= TESTCASES; testCase++){
char inputFileName[20] = "milk.inX";
inputFileName[7] = '1' +  (testCase - 1);
freopen(inputFileName, "r", stdin);
printf("\n#%d\n", testCase);
#endif

scanf("%d %d", &milkNeeded, &numOfFarmers);
int farmer;
for (farmer = 1; farmer <= numOfFarmers; farmer++)
scanf("%d %d", &farmers[farmer].price, &farmers[farmer].milk);

sortFarmersAccordingToPrice(1, numOfFarmers);

int minPrice = mix();

printf("%d\n", minPrice);

#if DEBUG
}
#endif
return 0;

}