usaco-guide/content/3_Bronze/6_Bronze_Pairs.md

slug	title	author	order
/bronze/pairs	Pairs & Tuples	Aaron Chew, Benjamin Qi, Nathan Wang, Darren Yao	6

A pair is a structure that holds two values, not necessarily of the same type.

(tuples?)

Of course, we can hold more than two values with something like pair<int,pair<int,int>>.

C++

Pair

• make_pair(a, b): Returns a pair with values a, b.
• pair.first: The first value of the pair.
• pair.second: The second value of the pair.

Example

#include <iostream>

using namespace std;

int main() {
  pair<string, int> myPair = make_pair("Testing", 123);
  cout << myPair.first << " " << myPair.second << endl; // Testing 123
  vector<pair<int,int>> v = {{2,4},{1,3},{3,4},{3,1}}; 
  sort(begin(v),end(v)); // {(1, 3), (2, 4), (3, 1), (3, 4)}
}

/* Output
 * Testing 123
 */

Tuple

(anyone use?)

Java

Unfortunately there is no default class for pairs in java, so you have to create your own.

class pair implements Comparable <pair>{
    int first;
    int second;
    public int compareTo(pair other) {
        return first==other.first?second-other.second:first-other.first;
    }
    pair(int a, int b) {
        first=a;
        second=b;
    }
}

If you have an array pair[]arr=new pair[100], make sure each element of this array is not null. You can call Arrays.sort(arr); on this array and it will sort it by all the first of the array and if there is a tie in first it will sort by second.

You can also use an int[] as a pair, or if you're using a pair of two different types, you can use Object[].

If you want to sort by 3 or more elements, it's a simple change. Just add a new variable in pair and make sure the comparable compares in the right order you want.