Subtask #1 过了 #0没过 望大佬求助

#include<bits/stdc++.h>
using namespace std;
int c,n,k,a[1000001],y[1000001] = {0},s = 0,b,j,tot = 0;
bool yn(int ok,int l){
    int num = 0;
    for(int i = 0;i <= c;i++){
        if(y[i] == 1) num = 0;
        else num++;
        if(num == l){
            num = 0;
            ok--;
        }
        if(ok < 0) break;
    }
    return ok >= 0;
}
int main(){
    cin>>c>>n>>k;
    b = c;
    for(int i = 1;i <= n;i++){
        cin>>a[i];
        y[a[i]]++;
    }
    while(s <= b){
        j = (s + b) / 2;
        if(yn(k,j)){
            b = j - 1;
            tot = j;
        }
        else{
            s = j + 1;
        }
    }
    if(tot == 0){
        int o = 0,maxn = -1;
        for(int i = 0;i <= c;i++){
            if(y[i] == 1){
                maxn = max(maxn,o);
            }
            else o++;
        }
        cout<<maxn;
    }
    else cout<<tot;
    return 0;
}