hdu 3624 (算术表达式求值)

/*
1、左递归可以用循环来实现,右递归可以用递归实现(也可以用循环实现,不过递归实现起来比较简单)
2、左递归实现左结合运算,右递归实现右结合运算
hdu 3624(网址: http://acm.hdu.edu.cn/showproblem.php?pid=3624 ) 的文法
exp         -> addTerm | exp addOp addTerm
addOp    -> + | -
addTerm -> mulTerm | addTerm mulOp mulTerm
mulOp     -> * | / | %
mulTerm -> eTerm ^ mulTerm | eTerm
eTerm    ->sNum | (exp)
sNum     -> num | -eTerm
*/
#include <stdio.h>
#include <memory>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <map>
#include <cmath>
#include <set>
#include <queue>
#include <time.h>
#include <limits>
using namespace std;
#define vType long long
#define MAXLEN 2005
const int vMax = 0x7fffffff;
const int vMin = ~vMax;
#define checkVal(val) (val >= vMin && val <= vMax)
char str[MAXLEN];
int pos, cnt; //pos为当前扫描位置,cnt为已经分配的节点的数目
char ch;  //ch为当前扫描的字符
struct treeNode{
    char op, flag; 
    vType val;
    treeNode* ch[2];
    void setFlag(){
        if((ch[0] && !ch[0]->flag) || (ch[1] && !ch[1]->flag)){
            flag = false;
        }
    }
}mem[MAXLEN*10];
treeNode* exp();
inline bool isDigit(char ch){
    return ch >= '0' && ch <= '9';
}
inline treeNode* newNode(){
    mem[cnt].flag = true;
    mem[cnt].op = ' ';  //op为空格表示不需要运算
    mem[cnt].ch[0] = mem[cnt].ch[1] = NULL;
    return &mem[cnt++];
}
treeNode* getSyntaxTree(){
    treeNode* tree;
    pos = cnt = 0;
    int i, j;
    i = j = 0;
    ch = '\n';
    do{  //忽略空格
        if(str[i] != ' ') str[j++] = str[i];
    }while(str[i++]);
 for(i = j = 0; str[i]; i++){ //加这一步是为了处理2000个(的变态数据
  if(str[i] == '(') j++;
  else if(str[i] == ')') j--;
 }
 if(j != 0){
  tree = newNode();
  tree->flag = false;
 }else tree = exp();
    return tree;
}
treeNode* eTerm(){
    treeNode* t;
    t = newNode();
    ch = str[pos++];
    if(ch == '('){
        t = exp();
        if(ch != ')') t->flag = false;
        else ch = str[pos++];
    }else if(isDigit(ch)){
        vType a = ch - '0';
        for(ch = str[pos++];isDigit(ch); ch = str[pos++]){
            if(t->flag){
                a = a * 10 + ch - '0';
            }
            if(!checkVal(a)){
                t->flag = false;
            }
        }
  t->val = a;
 }else if(ch == '-'){
  t->op = ch;
  t->ch[0] = newNode();
  t->ch[0]->val = 0;
  t->ch[1] = eTerm();
  t->setFlag();
 }else t->flag = false;
    return t;
}
treeNode* mulTerm(){
    treeNode *t, *p, *r, *t0, *t1;;
    r = t = eTerm();
 p = NULL;
    while(ch == '^'){ //循环实现右递归文法
  t1 = newNode();
  t1->op = ch;
  t1->ch[0] = t;
  t0 = eTerm();
  t1->ch[1] = t0;
  if(p){
   p->ch[1] = t1;
  }else r = t1;
  p = t1;
  t = t0;
    }
    return r;
}
treeNode* addTerm(){
    treeNode *t, *p;
    t = newNode();
    t->ch[0] = mulTerm();
    t->setFlag();
    while(ch == '*' || ch == '/' || ch == '%'){
        t->op = ch;
        t->ch[1] = mulTerm();
        t->setFlag();
        p = t;
        t = newNode();
        t->ch[0] = p;
    }
    return t;
}
treeNode* exp(){
    treeNode *t, *p;
    t = newNode();
    t->ch[0] = addTerm();
    while(ch == '-' || ch == '+'){
        t->op = ch;
        t->ch[1] = addTerm();
        p = t;
        t = newNode();
        t->ch[0] = p;
    }
    return t;
}
void cal(treeNode* root){
    if(!root) return;
    cal(root->ch[0]);
    cal(root->ch[1]);
    root->setFlag();
    if(!root->flag) return;
    if(root->op != ' '){
        vType a = 0;
        switch(root->op){
            case '-':
                a = root->ch[0]->val - root->ch[1]->val;
                break;
            case '+':
                a = root->ch[0]->val + root->ch[1]->val;
                break;
            case '*':
                a = root->ch[0]->val * root->ch[1]->val;
                break;
            case '/':
                if(root->ch[1]->val == 0){
                    root->flag = false;
                    return;
                }
                a = root->ch[0]->val / root->ch[1]->val;
                break;
            case '%':
                if(root->ch[1]->val == 0){
                    root->flag = 0;
                    return;
                }
                a = root->ch[0]->val % root->ch[1]->val;
                break;
            case '^':
    if(root->ch[1]->val < 0 || (root->ch[0]->val == 0 && root->ch[1]->val == 0)){
                    root->flag = false;
                    return;
                }
                double b = pow((double)root->ch[0]->val, (double)root->ch[1]->val);
                if(checkVal(b)) a = (vType)b;
                else{
                    root->flag = false;
                    return;
                }
                break;
        }
  if(checkVal(a)){
   root->val = a;
   root->setFlag();
  }else{
   root->flag = false;
  }
    }else if(root->ch[0]){
        root->flag = root->ch[0]->flag;
        root->val = root->ch[0]->val;
    }
}
int main(){
#ifndef ONLINE_JUDGE
 //freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
#endif
    int i, c;
    treeNode* root;
    scanf("%d", &c);
    getchar();
    for(i = 1; i <= c; i++){
        gets(str);
        root = getSyntaxTree();
        printf("Case %d: ", i);
        cal(root);
  if(root->flag){
   printf("%I64d\n", root->val);
  }
        else printf("ERROR!\n");
    }
    return 0;
}

 

posted on 2011-01-15 01:43 tw 阅读(529) 评论(0)  编辑 收藏 引用 所属分类: HDU题解


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