Coordinate Compression

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#1

Given n pairs of coordinates, how would you apply coordinate compression if the x and y coordinates don’t have to be distinct?

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#2

Here’s an easy way to do it (in the 1D case):

#include <iostream>
#include <vector>
#include <map>

int main() {
	std::map<int,int> m;
	std::vector<int> vals{4,4,2,-1,3,-1,-1};
	for (int v: vals) m[v];
	int label = 0; for (auto& p: m) p.second = label++;
	for (int& v: vals) v = m[v];
	for (int v: vals) std::cout << v << " ";
} // 3 3 1 0 2 0 0