二分查找 l=4 r=5 卡住的示范， ACM9817 Rangers

After leaving Canada you all head to Glacier Bay. You and Knave marvel at the beauty of the glaciers while Ark snickers about true beauty being found only in convex polygons and monotonic math functions, whatever that means.

You roll your eyes and follow him into the ranger station. The rangers are getting ready for a several day trip across glacier bay and are getting geared up. They have piles of tents, sleeping bags, etc strewn all over the floor and are arguing about who will go on the expedition.

The issue is that there are  rangers in the station and each ranger requires a certain amount of each piece of gear in order to go on the expedition. You suggest that they simply order more gear from Amazon, but there's also a budget for the expedition of  dollars.

You decide to help them figure out how to spend their money optimally such that as many rangers as possible are able to go. Given the number of rangers in the station, their current inventory of each piece of gear, the price of each piece of gear, and the gear requirements to send a single ranger can you print out how many pieces of each type they should order and the number of rangers that will be able to go?

Note that all rangers have the same gear requirements, that there is an infinite number of each piece of gear available for purchase, and that shipping is free since you have Amazon prime.

Input Format

The input will begin with 3 of integers, , , and , representing the number of rangers in the station (the maximum number of rangers that could go), the number of pieces of gear that must go with each ranger on the expedition, and the budget for the expedition.

 lines follow, each representing a piece of gear. Each line will start with a string containing only lowercase letters, the name of the piece of gear, . This will be followed by the number of that piece of gear that each ranger going requires , the number currently in stock , and the price of buying an additional piece of that gear .

Constraints

 for 33% of score
 for all cases
 
 
 
 
 

All gear names will contain only lowercase English letters.

Output Format

First print a single integer, the maximum number of rangers that will be able to go while staying in budget.

Next print the name of each piece of gear and the number that the ranger station should purchase, with each piece of gear being on a new line. The gear should appear alphabetized by name.

Sample Input 0

5 3 100tent 1 5 10lantern 2 12 6food 4 16 1

Sample Output 0

5food 4lantern 0tent 0

Explanation 0

There is enough room in the budget to add 4 food, in which case all of the rangers in the station can go on the expedition.

#include<bits/stdc++.h>using namespace std;typedef long long ll;struct node{    string nm;    ll x, y, z;    friend inline bool operator <(const node&a, const node &b){        return a.nm<b.nm;    }}a[120];ll n,m,cnt,R,G,D;ll vl, vr, vm, tot;int check(ll mid){tot=0;for (int i=0; i<G; i++){    if ((a[i].x*mid-a[i].y)>0) tot+=(a[i].x*mid-a[i].y)*a[i].z;}if (tot>D) return 1;if (tot==D) return 0;return -1;}vector<char>vec;int main(){cin>>R>>G>>D;for (int i=0; i<G; i++){    cin>>a[i].nm>>a[i].x>>a[i].y>>a[i].z;}vl=0; vr=R;while (vl<vr-1){    tot=0;    vm=(vl+vr)>>1;    int ret=check(vm);    if (ret==1) vr=vm;    else if (ret==-1) vl=vm;    else {        vl=vm; vr=vm;    }}int ret2=check(vr);if (ret2<1) vl=vr;cout<<vl<<endl;sort(a, a+G);for (int i=0; i<G; i++){    ll ans=vl*a[i].x-a[i].y;    if (ans<0) cout<<a[i].nm<<" "<<0<<endl;    else cout<<a[i].nm<<" "<<ans<<endl;}return 0;}

两个注意点，

第一个，整数的二分查找可能会卡住。比如，样例里，如果while (l<r) 然后vl=vm, vr=vm, 那么l取4 r取5 mid 是 4， 总价仍然小， l=vm 还是4。所以只能while (l<r-1)。

            对于这种连续函数只能取整数得，可以让r为不合法值，l为合法值， 然后用上述的while，最后check r是否合法。

第二个，function中的全局变量tot要初始化， 不初始化tot不是0.