Expression parsing

Resources:

Cp_Algorothm

Problem Link:

1309 - Children`s Math

1324 - Equivalent Boolean Expressions

Implementation:

	#include <bits/stdc++.h>
	using namespace std;
	#define INF 1<<30
	#define endl '\n'
	#define maxn 100005
	#define tc printf("Case %d: ", cs)
	#define tcn printf("Case %d:\n", cs);
	#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	typedef long long ll;
	const double PI = acos(-1.0);
	#define dbg1(x) cerr << #x << " = " << x << endl;
	#define dbg2(x, y) cerr << #x << " = " << x << ", " << #y << " = " << y << endl;
	#define dbg3(x, y, z) cerr << #x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl;
	#define dbg4(w,x, y, z) cerr << #w << " = " << w << ", " <<#x << " = " << x << ", " << #y << " = " << y << ", " << #z << " = " << z << endl;
	template < typename F, typename S >
	ostream& operator << ( ostream& os, const pair< F, S > & p ) {
	return os << "(" << p.first << ", " << p.second << ")";
	}
	template < typename T >
	ostream &operator << ( ostream & os, const vector< T > &v ) {
	os << "{";
	for (auto it = v.begin(); it != v.end(); ++it) {
	if ( it != v.begin() ) os << ", ";
	os << *it;
	}
	return os << "}";
	}
	template < typename T >
	ostream &operator << ( ostream & os, const set< T > &v ) {
	os << "[";
	for (auto it = v.begin(); it != v.end(); ++it) {
	if ( it != v.begin()) os << ", ";
	os << *it;
	}
	return os << "]";
	}
	template < typename F, typename S >
	ostream &operator << ( ostream & os, const map< F, S > &v ) {
	os << "[";
	for (auto it = v.begin(); it != v.end(); ++it) {
	if ( it != v.begin() ) os << ", ";
	os << it -> first << " = " << it -> second ;
	}
	return os << "]";
	}
	#define dbg(args...) do {cerr << #args << " : "; faltu(args); } while(0)
	clock_t tStart = clock();
	#define timeStamp dbg("Execution Time: ", (double)(clock() - tStart)/CLOCKS_PER_SEC)
	void faltu () { cerr << endl; }
	template <typename T>
	void faltu( T a[], int n ) {
	for (int i = 0; i < n; ++i) cerr << a[i] << ' ';
	cerr << endl;
	}
	template <typename T, typename ... hello>
	void faltu( T arg, const hello &... rest) { cerr << arg << ' '; faltu(rest...); }
	// Program showing a policy-based data structure.
	#include <ext/pb_ds/assoc_container.hpp> // Common file
	#include <ext/pb_ds/tree_policy.hpp>
	#include <functional> // for less
	#include <iostream>
	using namespace __gnu_pbds;
	using namespace std;
	// GNU link : https://goo.gl/WVDL6g
	typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
	tree_order_statistics_node_update>
	new_data_set;
	/**___________________________________________________**/
	bool delim(char c) {
	return c == ' ';
	}
	bool is_unary(char c) {
	return c == '+' || c == '-';
	}
	bool is_op(char c) {
	return c == '+' || c == '-' || c == '*' || c == '/';
	}
	int priority(char op)
	{
	if (op < 0) return 3;
	if (op == '+' || op == '-') return 1;
	if (op == '*' || op == '/') return 2;
	return -1;
	}
	void process_op(stack<int>& st, char op)
	{
	if (op < 0) {
	int l = st.top(); st.pop();
	switch (-op) {
	case '+': st.push(l); break;
	case '-': st.push(-l); break;
	}
	}
	else {
	int r = st.top(); st.pop();
	int l = st.top(); st.pop();
	switch (op) {
	case '+': st.push(l + r); break;
	case '-': st.push(l - r); break;
	case '*': st.push(l * r); break;
	case '/': st.push(l / r); break;
	}
	}
	}
	int evaluate(string& s)
	{
	stack<int> st;
	stack<char> op;
	bool may_be_unary = true;
	for (int i = 0; i < (int)s.size(); i++) {
	if (delim(s[i])) continue;
	if (s[i] == '(') {
	op.push('(');
	may_be_unary = true;
	}
	else if (s[i] == ')') {
	while (op.top() != '(') {
	process_op(st, op.top());
	op.pop();
	}
	op.pop();
	may_be_unary = false;
	}
	else if (is_op(s[i])) {
	char cur_op = s[i];
	if (may_be_unary && is_unary(cur_op)) cur_op = -cur_op;
	while (!op.empty() && (
	(cur_op >= 0 && priority(op.top()) >= priority(cur_op)) ||
	(cur_op < 0 && priority(op.top()) > priority(cur_op))
	)) {
	process_op(st, op.top());
	op.pop();
	}
	op.push(cur_op);
	may_be_unary = true;
	}
	else {
	int num = 0;
	while (i < (int)s.size() && isalnum(s[i]))
	num = num * 10 + s[i++] - '0';
	--i;
	st.push(num);
	may_be_unary = false;
	}
	}
	while (!op.empty()) {
	process_op(st, op.top()); op.pop();
	}
	return st.top();
	}
	int main()
	{
	FASTIO
	///*
	#ifndef ONLINE_JUDGE
	freopen("in.txt", "r", stdin);
	freopen("out.txt", "w", stdout);
	freopen("error.txt", "w", stderr);
	#endif
	//*/
	string s;
	cin >> s;
	cout << evaluate(s) << endl;
	}

view raw Expression parsing.cpp hosted with ❤ by GitHub

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