POJ Dreisam Equations-优快云博客

本文链接：https://blog.youkuaiyun.com/bobten2008/article/details/4523548

本文介绍了一种使用深度优先搜索(DFS)算法处理数学表达式的实现方法，通过递归地填充运算符来尝试所有可能的组合，以找到能使表达式等式成立的操作符配置。

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DFS + 表达式求值，输入处理很恶心

#include <iostream>
#include <memory>
#define MAX_N 100
using namespace std;

int exp[MAX_N + 1];
int curExp[MAX_N + 1];
int expLen, expVal, curVal;
int opType[3] = {-1, -2, -6};
bool found = false;

int stackv1[MAX_N + 1];
int stackv2[MAX_N + 1];
int head1;
int head2;

int trimParath()
{
    head1 = head2 = 0;
    int top, val1, val2;
    for(int i = 1; i <= expLen; i++)
    {
        int type = curExp[i];
        if(type >= 0)
            stackv1[head1++] = type;
        else
        {
            if(type == -3)
                stackv2[head2++] = type;
            else if(type == -1 || type == -2 || type == -6)
            {
                top = stackv2[head2 - 1];
                if(top == -3)
                    stackv2[head2++] = type;
                else if(top == -1 || top == -2 || top == -6)
                {
                    head2--;
                    val2 = stackv1[--head1];
                    val1 = stackv1[--head1];
                    if(top == -1) stackv1[head1++] = val1 + val2;
                    else if(top == -2) stackv1[head1++] = val1 - val2;
                    else if(top == -6) stackv1[head1++] = val1 * val2;
                    stackv2[head2++] = type;
                }
                else
                    stackv2[head2++] = type;
            }
            else if(type == -4)
            {
                top = stackv2[--head2];
                if(top == -1 || top == -2 || top == -6)
                {
                    val2 = stackv1[--head1];
                    val1 = stackv1[--head1];
                    if(top == -1) stackv1[head1++] = val1 + val2;
                    else if(top == -2) stackv1[head1++] = val1 - val2;
                    else if(top == -6) stackv1[head1++] = val1 * val2;
                    if(stackv2[head2 - 1] == -3)
                        head2--;
                }
            }
        }
    }
    while(head2 != 0)
    {
        top = stackv2[--head2];
        if(top == -1 || top == -2 || top == -6)
        {
            val2 = stackv1[--head1];
            val1 = stackv1[--head1];
            if(top == -1) stackv1[head1++] = val1 + val2;
            else if(top == -2) stackv1[head1++] = val1 - val2;
            else if(top == -6) stackv1[head1++] = val1 * val2;
        }
    }
    return stackv1[0];
}

void dfsT(int curPos)
{
    if(found)
        return;
    if(curPos > expLen)
    {
        if(curExp[4] == -6 && curExp[6] == -2 && curExp[8] == -6)
        {
            int a = 2;
        }
        int res = trimParath();
        if(res == expVal)
            found = true;
        return;
    }
    if(exp[curPos] != -5 && !found)
    {
        curExp[curPos] = exp[curPos];
        dfsT(curPos + 1);
        return;
    }
    for(int i = 0; i < 3 && !found; i++)
    {
        curExp[curPos] = opType[i];
        dfsT(curPos + 1);
    }
}
int main()
{
    char ch;
    int seq = 0;
    bool neg = false;
    while((ch = getchar()) != '0')
    {
        seq ++, found = neg = false;
        expVal = 0;
        while(ch == ' ')
            ch = getchar();
        if(ch == '-')
            neg = true;
        else
            expVal = int(ch - '0');
        while((ch = getchar()) != ' ' && ch != '=')
            expVal = expVal * 10 + int(ch - '0');

        if(neg)
            expVal = -expVal;

        if(ch != '=') while((ch = getchar()) != '=');
        while((ch = getchar()) == ' ');

        bool preDigit = false;
        bool firstV = true;
        curVal = 0, expLen = 0;

        bool allEven = true;

        while(ch != 10)
        {
            if(ch >= '0' && ch <= '9')
            {
                preDigit = true;
                curVal = curVal * 10 + int(ch - '0');

                if(firstV && expLen >= 1 && (exp[expLen] >=0 || exp[expLen] == -4))
                    exp[++expLen] = -5;
                firstV = false;
            }
            else
            {
                firstV = true;
                if(preDigit)
                {
                    exp[++expLen] = curVal;

                    if(curVal % 2 != 0)
                        allEven = false;
                    curVal = 0;
                    preDigit = false;
                }
                if(ch == '(')
                {
                    if(expLen >= 1 && (exp[expLen] == -4 || exp[expLen] >= 0))
                        exp[++expLen] = -5;
                    exp[++expLen] = -3;
                }
                else if(ch == ')')
                    exp[++expLen] = -4;
            }
            ch = getchar();
        }
        if(preDigit)
        {
            exp[++expLen] = curVal;
            if(curVal % 2 != 0)
                allEven = false;
        }

        cout<<"Equation #"<<seq<<":"<<endl;

        dfsT(1);
        if(found)
        {
            //printf("%I64d=", expVal);
            cout<<expVal<<"=";
            for(int i = 1; i <= expLen; i++)
            {
                int type = curExp[i];
                if(type >= 0)
                    cout<<type;
                    //printf("%I64d", type);
                else
                {
                    if(type == -1)
                        cout<<"+";
                    else if(type == -2)
                        cout<<"-";
                    else if(type == -3)
                        cout<<"(";
                    else if(type == -4)
                        cout<<")";
                    else if(type == -6)
                        cout<<"*";
                }
            }
        }
        else
            cout<<"Impossible";
        cout<<endl<<endl;
    }
    return 0;
}