Contents

# 1. 题目

http://poj.org/problem?id=2456

Aggressive cows
 Time Limit: 1000MS Memory Limit: 65536K Total Submissions: 8456 Accepted: 4224

Description

Farmer John has built a new long barn, with N (2 <= N <= 100,000) stalls. The stalls are located along a straight line at positions x1,…,xN (0 <= xi <= 1,000,000,000).

His C (2 <= C <= N) cows don’t like this barn layout and become aggressive towards each other once put into a stall. To prevent the cows from hurting each other, FJ want to assign the cows to the stalls, such that the minimum distance between any two of them is as large as possible. What is the largest minimum distance?

Input

* Line 1: Two space-separated integers: N and C

* Lines 2..N+1: Line i+1 contains an integer stall location, xi

Output

* Line 1: One integer: the largest minimum distance

Sample Input

5 3
1
2
8
4
9

Sample Output

3

Hint

OUTPUT DETAILS:

FJ can put his 3 cows in the stalls at positions 1, 4 and 8, resulting in a minimum distance of 3.

Huge input data,scanf is recommended.

Source

# 3. 代码

#include <stdio.h>
#include <stdlib.h>

#define MAX_N 100000

void solveE5B_AggressiveCows();
void inputPositions(int pos[], int n);
int cmp(const void *a, const void *b);
bool isSafe(int pos[], int n, int dist, int target);

int main() {
solveE5B_AggressiveCows();
}

int positions[MAX_N];
void solveE5B_AggressiveCows() {
int n, c;
scanf("%d %d", &n, &c);

inputPositions(positions, n);

int l = 0, r = positions[n - 1], mid = (l + r) / 2;
while (l <= r) {
if (isSafe(positions, n, mid, c)) {
l = mid + 1;
} else {
r = mid - 1;
}
mid = (l + r) / 2;
}

printf("%d\n", mid);
}

void inputPositions(int pos[], int n) {
for (int i = 0; i < n; ++i) {
scanf("%d", &pos[i]);
}
qsort(pos, n, sizeof(int), cmp);
}

int cmp(const void *a, const void *b) {
return (*(int *)a - *(int *)b);
}

bool isSafe(int pos[], int n, int dist, int target) {
int cnt = 1, start = pos;
for (int i = 1; i < n; ++i) {
if (pos[i] - start >= dist) {
start = pos[i];
++cnt;
}
}

if (cnt >= target)
return true;
else
return false;
}