数据结构的入门题，理解倒是不复杂，用两个栈就行（一个存数字一个存符号）。对于我这样的弱弱没事练练编码能力还是不错的。
注意运算优先级即可。（过两天回科大了，下次再做题也不知道何时，ACM生涯两铜收场orz）
题目链接：
http://hihocoder.com/contest/hihointerview11/problem/3
代码：
1 #include <bits/stdc++.h> 2 3 using namespace std; 4 typedef long long int64; 5 6 stack<int64> sn; 7 stack<char> sc; 8 9 const int maxn = 100 + 10; 10 char str[maxn]; 11 12 char op[] = { '+', '-', '*', '/', '(', ')', '#' }; 13 14 int getOpId(char op){ 15 if(op == '+') 16 return -1; 17 else if(op == '-') 18 return -2; 19 else if(op == '*') 20 return -3; 21 else if(op == '/') 22 return -4; 23 else if(op == '(' ) 24 return -5; 25 else if(op == ')' ) 26 return -6; 27 else if(op == '#') 28 return -7; 29 else if(op == '&') 30 return -8; 31 } 32 33 vector<int64> v; 34 35 int getPrio(char op){ 36 switch(op){ 37 case '+': return 3; 38 case '-': return 3; 39 case '*': return 4; 40 case '/': return 4; 41 case '(': return 2; 42 case '&': return 0; 43 default: return 1; 44 } 45 } 46 47 int64 cal(int64 a, int64 b, char opt){ 48 if(opt == '+'){ 49 return a+b; 50 }else if(opt == '-'){ 51 return a-b; 52 }else if(opt == '*'){ 53 return a*b; 54 }else if(opt == '/'){ 55 return a/b; 56 } 57 } 58 59 int main(void){ 60 scanf("%s", str); 61 int len = strlen(str); 62 str[len++] = '#'; 63 64 for(int i = 0; i < len; ++i){ 65 if('0' <= str[i] && str[i] <= '9'){ 66 int64 t = 0; 67 while('0' <= str[i] && str[i] <= '9'){ 68 t = t * 10 + (str[i] - '0'); 69 i++; 70 } 71 i--; 72 v.push_back(t); 73 }else{ 74 v.push_back(getOpId(str[i])); 75 } 76 //cout << v.back() << " "; 77 } 78 //cout << endl; 79 80 int sz = v.size(); 81 sc.push('&'); 82 for(int i = 0; i < sz; ++i){ 83 if(v[i] >= 0){ 84 sn.push(v[i]); 85 //cout << "push " << v[i] << endl; 86 }else{ 87 char c = op[-v[i]-1]; 88 if(c == '('){ 89 sc.push('('); 90 //cout << "push " << '(' << endl; 91 }else if(c == ')'){ 92 while(sc.top() != '('){ 93 int64 b = sn.top(); sn.pop(); 94 int64 a = sn.top(); sn.pop(); 95 char opt = sc.top(); sc.pop(); 96 sn.push(cal(a, b, opt)); 97 //cout << "cal " << a << " " << opt << " " << b << endl; 98 } 99 sc.pop(); 100 //cout << "pop " << '(' << endl; 101 }else{ 102 int prio1 = getPrio(c); 103 int prio2; 104 105 while(prio1 <= (prio2 = getPrio(sc.top()))){ 106 //cout << "prio1: " << prio1 << " prio2: " << prio2 << endl; 107 int64 b = sn.top(); sn.pop(); 108 int64 a = sn.top(); sn.pop(); 109 char opt = sc.top(); sc.pop(); 110 sn.push(cal(a, b, opt)); 111 //cout << "cal " << a << " " << opt << " " << b << endl; 112 } 113 sc.push(c); 114 //cout << "push " << c << endl; 115 } 116 } 117 } 118 119 //cout << "haha" << endl; 120 printf("%lld ", sn.top()); 121 122 return 0; 123 } 124 125 /** 126 5*(3+8*2)-(5+6*2-7)*2 127 100*(2+12)-(20/3)*2 128 (8+2*3/4-4)*(3-2+5/2*3)*(3-4+3)/6 129 */