ZOJ-2483

来源：互联网发布：淘宝网电子琴编辑：程序博客网时间：2024/06/06 09:44

又是一道题搞了一个晚上。。各中滋味难以言表，无限WA。。。开始用C，是先转后缀表达式再求值的，逻辑有错误，我以为栈哪里用错了，换JAVA搞，一样的算法，Runtime Error了，肯定是抛空栈异常了，肯定有比较变态的测试数据。。翻了翻大牛的题解，说有!!!!V这种数据，好吧，一运行果断报错了，然后就慢慢改，对于取反操作的处理和其他两个不大一样，和括号的处理有点像，就是如果读入一个数字，就判断前面是否有取反符号，直接算掉，还有就是当一个括号计算完之后，如果前面有取反符号，还是先把取反符号的操作算掉。。还好最后逻辑总算对了，真艰难啊。。

import java.util.Scanner;import java.util.Stack;public class Main{static boolean convert(String s){Stack<Character> op = new Stack<Character>();Stack<Boolean> num = new Stack<Boolean>();for (char c : s.toCharArray()){if (c == ' ')continue;else if (c == 'F' || c == 'V'){num.push(c == 'V');while (!op.isEmpty() && op.peek() == '!')calc(num, op.pop());}else if (c == '(' || c == '!')op.push(c);else if (c == ')'){while (op.peek() != '(')calc(num, op.pop());op.pop();while (!op.isEmpty() && op.peek() == '!')calc(num, op.pop());}else if (c == '|'){while (!op.isEmpty() && op.peek() != '(')calc(num, op.pop());op.push(c);}else if (c == '&'){while (!op.isEmpty() && op.peek() != '(' && op.peek() != '|')calc(num, op.pop());op.push(c);}}while (!op.isEmpty())calc(num, op.pop());return num.pop();}static void calc(Stack<Boolean> num, char op){boolean a, b;if (op == '!'){a = num.pop();num.push(!a);}else if (op == '|'){a = num.pop();b = num.pop();num.push(a || b);}else{a = num.pop();b = num.pop();num.push(a && b);}}public static void main(String[] args){Scanner sc = new Scanner(System.in);int count = 0;while (sc.hasNextLine()){String line = sc.nextLine();System.out.format("Expression %d: %s\n", ++count,convert(line) ? "V" : "F");}sc.close();}}

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