roman num. to int.cpp

/*
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//Question/Info

Roman Number to Integer
Easy Accuracy: 49.66% Submissions: 19152 Points: 2
Given a string in roman no format (s)  your task is to convert it to an integer . Various symbols and their values are given below.
I 1
V 5
X 10
L 50
C 100
D 500
M 1000

Example 1:

Input:
s = V
Output: 5
Example 2:

Input:
s = III
Output: 3
Your Task:
Complete the function romanToDecimal() which takes an string as input parameter and returns the equivalent decimal number.

Expected Time Complexity: O(|S|), |S| = length of string S.
Expected Auxiliary Space: O(1)

Constraints:
1<=roman no range<=3999



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author: srj_v
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*/

#include <bits/stdc++.h>
using namespace std;

#define _IOS   ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

typedef long double ld;
typedef long long int lli;

#pragma GCC optimize("Ofast")

void c_p_c()
{
#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
}

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int32_t main() {
///////////
//	c_p_c();
///////////
	_IOS
//////////

	// code

	/*
	int t ; cin >> t; while(t--){}
	*/


	int romanToDecimal(string & str) {
		// code here

		unordered_map<char, int> mp;
		mp['I'] = 1;
		mp['V'] = 5;
		mp['X'] = 10;
		mp['L'] = 50;
		mp['C'] = 100;
		mp['D'] = 500;
		mp['M'] = 1000;

		int n = str.size();

		int num = mp[str[n - 1]];
		for (int i = n - 2; i >= 0; i--) {
			if (mp[str[i]] < mp[str[i + 1]]) num -= mp[str[i]];
			else num += mp[str[i]];
		}
		return num;

	}



// cerr << "time: " << clock() << " ms" << '\n';
	return 0;
}

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