CodeForces 416A_codeforces - 416a-优快云博客

本文针对一道ACM编程题中的错误进行了修正，主要问题在于MAX值的不当定义及未考虑负数情况。通过调整MAX值并完善边界条件处理，解决了原有程序中存在的问题。

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这道题，有两个错误。一个是：没有测试负数的情况；另一个也是核心错误就是MAX不应该定义成 2000000001 而应该定义成 2000000000，最后取余的时候可以用(MAX + 1)。

Wa：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
using namespace std;
#define MAX 2000000001
int nasce,num,length,Max,Min;
string ope;
char ans;
int main()
{
    while(scanf("%d",&nasce) != EOF)
    {
        Min = -MAX;
        Max = MAX;
        while(nasce--)
        {
            cin >> ope >> num >> ans;
            if(ans == 'Y')
            {
                if(ope == ">")
                    Min = max(++num,Min);
                else
                    if(ope == "<")
                        Max = min(--num,Max);
                    else
                        if(ope == ">=")
                            Min = max(num,Min);
                        else
                            if(ope == "<=")
                                Max = min(num,Max);
            }
            else
            {
                if(ope == ">")
                    Max = min(num,Max);
                else
                    if(ope == "<")
                        Min = max(num,Min);
                    else
                        if(ope == ">=")
                            Max = min(--num,Max);
                        else
                            if(ope == "<=")
                                Min = max(++num,Min);

            }
        }
        //cout << Min << ' ' << Max << ' ' << num << endl;
        if(Max >= Min)
            cout << Min % MAX<< endl;
        else
            cout << "Impossible" << endl;
    }
    return 0;
}

Ac:

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
using namespace std;
#define MAX 2000000000
int nasce,num,length,Max,Min;
string ope;
char ans;
int main()
{
    while(scanf("%d",&nasce) != EOF)
    {
        Min = -MAX;
        Max = MAX;
        while(nasce--)
        {
            cin >> ope >> num >> ans;
            if(ans == 'Y')
            {
                if(ope == ">")
                    Min = max(++num,Min);
                else
                    if(ope == "<")
                        Max = min(--num,Max);
                    else
                        if(ope == ">=")
                            Min = max(num,Min);
                        else
                            if(ope == "<=")
                                Max = min(num,Max);
            }
            else
            {
                if(ope == ">")
                    Max = min(num,Max);
                else
                    if(ope == "<")
                        Min = max(num,Min);
                    else
                        if(ope == ">=")
                            Max = min(--num,Max);
                        else
                            if(ope == "<=")
                                Min = max(++num,Min);

            }
        }
        //cout << Min << ' ' << Max << ' ' << num << endl;
        if(Max >= Min)
            cout << Min % (MAX + 1) << endl;
        else
            cout << "Impossible" << endl;
    }
    return 0;
}