Codeforces 864 C Bus 思维

#include <iostream>
#include <cstdio>
#include <map>
#include <iterator>
#include <string>
using namespace std;

const int maxn = 1e4+100;
int dis[maxn];

int main() {
    int a, b, f, k;
    cin >> a >> b >> f >> k;
    int temp1 = f;
    int temp2 = a-f;
    temp1 *= 2, temp2 *= 2;
    dis[1] = f;
    int flag = 0;
    if( k & 1 ) flag = 1;
    if( flag == 1 ) {
        dis[k+1] = a-f;
        int temp = 1;
        for( int i = 2; i <= k; i++ ) {
            if( temp==1 ) {
                dis[i] = temp2;
            }
            else {
                dis[i] = temp1;
            }
            temp = -temp;
        }
    }
    else {
        dis[k+1] = f;
        int temp = 1;
        for( int i = 2; i <= k; i++ ) {
            if( temp==1 ) {
                dis[i] = temp2;
            }
            else {
                dis[i] = temp1;
            }
            temp = -temp;
        }
    }
//    for( int i = 1; i <= k+1; i++ ) {
//        cout << dis[i] << " ";
//    }
//    cout << endl;

    int ans = 0;
    flag = 0;
    int temp = 0;
    for( int i = 1; i <= k+1; i++ ) {
        if( dis[i] > b ) {
            flag = 1;
            break;
        }
        if( temp + dis[i] <= b ) {
            temp += dis[i];
        }
        else {
            temp = dis[i];
            ans ++;
        }
    }
    if( flag ) {
        cout << "-1" << endl;
    }
    else {
        cout << ans << endl;
    }
    return 0;
}