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partition-array.cc
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partition-array.cc
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// Copyright (c) 2015 Elements of Programming Interviews. All rights reserved.
#include <algorithm>
#include <cassert>
#include <functional>
#include <iostream>
#include <random>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using std::cout;
using std::default_random_engine;
using std::endl;
using std::hash;
using std::max;
using std::random_device;
using std::swap;
using std::string;
using std::uniform_int_distribution;
using std::unordered_map;
using std::unordered_set;
using std::vector;
// @include
struct Person {
int age;
string name;
};
void GroupByAge(vector<Person>* person_array) {
unordered_map<int, int> age_to_count;
for (const Person& p : *person_array) {
++age_to_count[p.age];
}
unordered_map<int, int> age_to_offset;
int offset = 0;
for (const auto& p : age_to_count) {
age_to_offset[p.first] = offset;
offset += p.second;
}
while (age_to_offset.size()) {
auto from = age_to_offset.begin();
auto to = age_to_offset.find((*person_array)[from->second].age);
swap((*person_array)[from->second], (*person_array)[to->second]);
// Use age_to_count to see when we are finished with a particular age.
--age_to_count[to->first];
if (age_to_count[to->first] > 0) {
++to->second;
} else {
age_to_offset.erase(to);
}
}
}
// @exclude
string RandString(int len) {
string ret;
default_random_engine gen((random_device())());
uniform_int_distribution<int> char_dis(0, 25);
while (len--) {
ret += 'a' + char_dis(gen);
}
return ret;
}
static void SimpleTest() {
vector<Person> people = {Person({20, "foo"}), Person({10, "bar"}),
Person({20, "widget"}), Person({20, "something"})};
GroupByAge(&people);
if (people[0].age == 10) {
assert(people[1].age == 20 && people[2].age == 20 && people[3].age == 20);
} else {
assert(people[1].age == 20 && people[2].age == 20 && people[3].age == 10);
}
}
int main(int argc, char* argv[]) {
SimpleTest();
default_random_engine gen((random_device())());
for (int times = 0; times < 1000; ++times) {
int size;
if (argc == 2 || argc == 3) {
size = atoi(argv[1]);
} else {
uniform_int_distribution<int> dis(1, 10000);
size = dis(gen);
}
int k;
if (argc == 3) {
k = atoi(argv[2]);
} else {
uniform_int_distribution<int> dis(1, size);
k = dis(gen);
}
vector<Person> person_array;
uniform_int_distribution<int> k_dis(0, k - 1);
uniform_int_distribution<int> len_dis(1, 10);
for (int i = 0; i < size; ++i) {
person_array.emplace_back(Person{k_dis(gen), RandString(len_dis(gen))});
}
unordered_set<int> age_set;
for (const Person& p : person_array) {
age_set.emplace(p.age);
}
GroupByAge(&person_array);
// Check the correctness of sorting.
int diff_count = 1;
for (int i = 1; i < person_array.size(); ++i) {
if (person_array[i].age != person_array[i - 1].age) {
++diff_count;
}
}
assert(diff_count == age_set.size());
}
return 0;
}