HDU 1686 Lazy Math Instructor（中缀转后缀，栈模拟）

ACM

题目地址：POJ 1686 Lazy Math Instructor

题意： 
问两个等式是否相等。

分析： 
栈模拟把中缀转后缀，然后用后缀算出值，再进行比较。 
直接把字母看成ASCII值就行了。

代码：

/**  Author:      illuz <iilluzen[at]gmail.com>*  Blog:        http://blog.csdn.net/hcbbt*  File:        1686.cpp*  Create Date: 2014-08-04 20:05:00*  Descripton:  simulate, expression */#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>#include <algorithm>#include <stack>using namespace std;const int N = 90;int prior(char c) {    if(c == '(')        return 0;    else if (c == '*')        return 2;    else        return 1;}void convert(char* s, char* tmp) {int len = strlen(s), n = 0;int res, rhs, lhs;stack<int> st;for (int i = 0; i < len; i++) {char r = s[i];if (r == ' ')continue;if ((r >= 'a' && r <= 'z') || (r >= '0' && r <= '9'))tmp[n++] = r;else {if (st.empty() || r == '(')st.push(r);else if (r == ')') {while (!st.empty() && st.top() != '(') {tmp[n++] = st.top();st.pop();}st.pop();} else {while (!st.empty() && prior(r) <= prior(st.top())) {tmp[n++] = st.top();st.pop();}st.push(r);}}}while (!st.empty()) {tmp[n++] = st.top();st.pop();}tmp[n] = 0;}int calc(char* t) {int len = strlen(t);int rhs = 0, lhs = 0;stack<int> st;for (int i = 0; i < len; i++) {if (t[i] >= '0' && t[i] <= '9') st.push(t[i] - '0');else if (t[i] <= 'z' && t[i] >= 'a')st.push(t[i]);else {rhs = st.top();st.pop();lhs = st.top();st.pop();if (t[i] == '+')st.push(rhs + lhs);else if (t[i] == '-')st.push(lhs - rhs);elsest.push(rhs * lhs);}}return st.top();}int main() {char str[N], temp[N];int n;scanf("%d\n",&n);while (n--) {gets(str);convert(str, temp);int ans1 = calc(temp);gets(str);convert(str, temp);int ans2 = calc(temp);if (ans1 == ans2)printf("YES\n");elseprintf("NO\n");}}