数据结构08——逆波兰式

Time Limit: 3000ms, Memory Limit: 10000KB , Accepted: 277, Total Submissions: 763

Description

假设表达式由单字母变量和双目四则运算算符构成。试编写程序，将一个通常书写形式且书写正确的表达式转换为逆波兰式。

Input

输入由单字母变量和双目四则运算算符构成的表达式。

Output

输出其逆波兰式。

• Sample Input 

  (a+b)*c

• Sample Output

  ab+c*

• #include<stdio.h>
  #include<stdlib.h>
  
  typedef struct stack{
  	struct stack *pop;
  	struct stack *bottom;
  	struct stack *next;
  	char sign;
  }stack; 
  
  void init(stack *list){
      list->bottom = (stack*) malloc (sizeof(stack));
  	list->bottom->next = NULL;
  	list->pop = list->bottom;
  }
  
  void push(stack *list, char s){
      stack *p;
  	p = (stack*)malloc(sizeof(stack));
  	p->sign = s;
  	p->next = list->pop;
  	list->pop = p;
  }
  
  bool judge(char a, char b){
      if((a == '*' && (b == '+' || b == '-')) || (a == '/' && (b == '+' || b == '-')))
  		return true;
  	else
  		return false;
  }
  
  void pop(stack *list){
      stack *p;
  	p = list->pop;
  	list->pop = list->pop->next;
  	free(p);
  }
  
  int main(){
  	char s,t;
  	stack *list;
  	list = (stack*) malloc (sizeof(stack));
  	init(list);
  	while(scanf("%c",&s) && s!='\n'){
  		if(s >= 'a' && s <= 'z'){
  		    printf("%c",s);
  		}
  		else if(s == '('){
  		    push(list,s);
  		}
  		else if(s == ')'){
  			while(list->pop->sign != '('){
  				printf("%c",list->pop->sign);
  			    pop(list);
  			}
  			pop(list);
  		}
  		else{
  			while(1){
  				t=list->pop->sign;
  			    if(judge(s, list->pop->sign) || list->pop == list->bottom || list->pop->sign == '('){
  		            push(list, s);
  					break;
  		        }
  				else if(t == '+' || t == '-' || t == '*' || t == '/'){
  				    printf("%c",list->pop->sign);
  			        pop(list);
  				}
  				else{
  					break;
  				}
  			}   
  		}
  	}
      while(list->pop != list->bottom){
      	printf("%c",list->pop->sign);
  		pop(list);
      }
      printf("\n");
  	return 0;
  }