POJ2456 Aggressive cows

　　Aggressive cows

　　二分，关键是转化为二分！

#include <cstdio>
#include <algorithm>
const int maxn = 1000000005;
const int maxN = 100005;

int N, C;
int a[maxN];
using namespace std;
bool judge(int x) {
    int s = 0;
    for (int i = 1; i < C;i++) {
        int ctr = s+1;
        while (ctr < N && (a[ctr]-a[s] < x)) {
            ctr++;
        }
        if (ctr==N) {
            return false;
        }
        s = ctr;
    }
    return true;
}
int main(void)
{
    scanf("%d%d", &N, &C);
    for (int i = 0; i < N; i++) {
        scanf("%d", &a[i]);
    }
    sort(a, a+N);
    int l = 0, u = maxn, mid;
    for (;(u-l)>1;){
        mid = (l+u)/2;
        if (judge(mid)) {
            l = mid;
        } else {
            u = mid;
        }
    }
    printf("%d\n", l);
    return 0;
}