HDU 4004:The annual Games(答案二分)

难在judge函数的编写，之前写了个复杂度n的judge函数。。。妥妥的TLE了

#include"cstdio"
#include"cmath"
#include"algorithm"
#include"cstring"
#define MAXN 500010
using namespace std;
int n,step,len,ans;
int stone[MAXN];
bool judge(int abi)
{   int temp=0,l,mark=0,t;
    for(int i=0;i<=step;i++){
        while(temp+abi>=stone[mark]&&mark<=n)
            t=stone[mark++];
        temp=t;
        if(temp>=len) return true;
    }
    if(temp>=len) return true;
    return false;
}
int get_ans()
{   int low=0,high=len,mid;
    while(high>=low){
    mid=low+(high-low)/2;
    if(judge(mid)) high=mid-1;
    else low=mid+1;
    }
    return mid;
}
int main()
{   while(scanf("%d%d%d",&len,&n,&step)!=EOF){
        for(int i=0;i<n;i++) scanf("%d",&stone[i]);
        stone[n]=len;
        sort(stone,stone+n);
        printf("%d\n",get_ans());
    }
    return 0;
}