# Tree calculator

Nov 25th, 2020 (edited)
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1. #include <bits/stdc++.h>
2.
3. using namespace std;
4.
5. int priority(char op)
6. {
7.     if (op == '+' or op == '-')
8.         return 1;
9.     if (op == '*' or op == '/')
10.         return 2;
11.     return 100 - isdigit(op);
12. }
13.
14. int last_op(string exp, int left, int right)
15. {
16.     int min = 100;
17.     int res = left;
18.     for (int i = left; i <= right; i++)
19.     {
20.         int tmp = priority(exp[i]);
21.         if (tmp <= min)
22.         {
23.             min = tmp;
24.             res = i;
25.         }
26.     }
27.     return res;
28. }
29.
30. struct Tree
31. {
32. private:
33.     char op;
34.     Tree *l, *r;
35.
36. public:
37.     Tree(string exp, int left, int right);
38.     double calc();
39.     void clear();
40.     ~Tree();
41. };
42.
43. Tree::Tree(string exp, int left, int right)
44. {
45.     int last = last_op(exp, left, right);
46.     this->op = exp[last];
47.     if (isdigit(this->op))
48.         return;
49.     this->l = new Tree(exp, left, last - 1);
50.     this->r = new Tree(exp, last + 1, right);
51. }
52.
53. double Tree::calc()
54. {
55.     double res = 0;
56.     if (isdigit(this->op))
57.         res = this->op - '0';
58.     else
59.     {
60.         if (this->op == '+')
61.             res = l->calc() + r->calc();
62.         if (this->op == '-')
63.             res = l->calc() - r->calc();
64.         if (this->op == '*')
65.             res = l->calc() * r->calc();
66.         if (this->op == '/')
67.             res = l->calc() / r->calc();
68.     }
69.     return res;
70. }
71.
72. void Tree::clear()
73. {
74.     if (isdigit(this->op))
75.     {
76.         delete this;
77.         return;
78.     }
79.     l->clear();
80.     r->clear();
81.     delete this;
82. }
83.
84. Tree::~Tree() { this->clear(); }
85.
86. int main()
87. {
88.     // 1 + 3 * 4 - 5 * 8 / 2 + 1 + 6 * 9 / 3
89.     // 3 * 4 - 5 * 8
90.     string exp;
91.     getline(cin, exp);
92.     Tree *t = new Tree(exp, 0, exp.size() - 1);
93.     cout << t->calc() << '\n';
94.     return 0;
95. }
96.
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