update solution to ugly number II

Author: derekharrison

264. Ugly Number II/ugly-number-II/main.cpp

@@ -7,91 +7,40 @@
 
 #include <iostream>
 #include <map>
+#include <set>
+#include <unordered_map>
 #include <vector>
 
 using namespace std;
 
-void merge(vector<int> & arr, int i, int k, int j) {
-
- int n1 = k - i + 1;
- int n2 = j - k;
- int* arr1 = new int[n1 + 1];
- int* arr2 = new int[n2 + 1];
- int arr_index = i;
- for(int arr1_index = 0; arr1_index < n1; ++arr1_index) {
- arr1[arr1_index] = arr[arr_index];
- arr_index++;
- }
-
- for(int arr2_index = 0; arr2_index < n2; ++arr2_index) {
- arr2[arr2_index] = arr[arr_index];
- arr_index++;
- }
-
- arr1[n1] = INT_MAX;
- arr2[n2] = INT_MAX;
-
- int arr1_index = 0;
- int arr2_index = 0;
- for(int arr_index = i; arr_index <= j; ++arr_index) {
- if(arr1[arr1_index] >= arr2[arr2_index]) {
- arr[arr_index] = arr2[arr2_index];
- arr2_index++;
- }
- else {
- arr[arr_index] = arr1[arr1_index];
- arr1_index++;
- }
- }
-
- //Free data
- delete [] arr1;
- delete [] arr2;
-}
-
-void merge_sort(vector<int> & arr, int i, int j) {
-
- if(j - i > 0) {
- int k = (i + j) / 2;
- merge_sort(arr, i, k);
- merge_sort(arr, k + 1, j);
- merge(arr, i, k, j);
- }
-}
-
-void merge_sort_wrap(vector<int> & input_arr) {
-
- int n = (int) input_arr.size();
-
- //Perform sort
- merge_sort(input_arr, 0, n - 1);
-}
-
-void gen_numbers(long t, vector<int> & uglies, int n, long cap, map<long, long> & dp) {
+void gen_numbers(long t, set<int> & uglies, long cap, unordered_map<long, long> & dp) {
 
+ // If uglies derived from t have been computed do not proceed with computation
  if(dp[t] != 0) {
  return;
  }
 
+ // Compute all uglies less than cap
  if(t < cap) {
  long val1 = t * 2;
  long val2 = t * 3;
  long val3 = t * 5;
 
  if(val1 < cap) {
- uglies.push_back((int) val1);
- gen_numbers(val1, uglies, n, cap, dp);
+ uglies.insert((int) val1);
+ gen_numbers(val1, uglies, cap, dp);
  }
  if(val2 < cap) {
- uglies.push_back((int) val2);
- gen_numbers(val2, uglies, n, cap, dp);
+ uglies.insert((int) val2);
+ gen_numbers(val2, uglies, cap, dp);
  }
  if(val3 < cap) {
- uglies.push_back((int) val3);
- gen_numbers(val3, uglies, n, cap, dp);
+ uglies.insert((int) val3);
+ gen_numbers(val3, uglies, cap, dp);
  }
  }
 
+ // Set flag signaling uglies derived from t have been computed
  dp[t] = 1;
 }
 
@@ -100,38 +49,22 @@ int ugly_number_api(int n) {
  // Results are integers, and so ugly numbers are <= INT_MAX
  long cap = INT_MAX;
 
- // Reduce cap for moderate numbers of n. Maximum value of n = 1690
- if(1000 < n && n <= 1250) {
- cap = cap / 9;
- }
- if(n <= 1000) {
- cap = cap / 40;
- }
- 
  // Storage for ugly numbers
- vector<int> uglies;
- uglies.push_back(1);
+ set<int> uglies_set;
+ uglies_set.insert(1);
 
  // Memo table
- map<long, long> dp;
+ unordered_map<long, long> dp;
 
  // Generate ugly numbers
- gen_numbers(1, uglies, n, cap, dp);
+ gen_numbers(1, uglies_set, cap, dp);
 
- // Sort array of ugly numbers
- merge_sort_wrap(uglies);
+ // Get nth element in ugly number set
+ set<int>::iterator it = uglies_set.begin();
+ advance(it, n - 1);
+ int x = *it;
 
- // Remove duplicate ugly numbers
- vector<int> set_arr;
- int size_uglies = (int) uglies.size();
- 
- for(int i = 0; i < size_uglies - 1; ++i) {
- if(uglies[i + 1] != uglies[i]) {
- set_arr.push_back(uglies[i]);
- }
- }
- 
- return set_arr[n - 1];
+ return x;
 }
 
 int main(int argc, const char * argv[]) {
@@ -146,4 +79,4 @@ int main(int argc, const char * argv[]) {
  cout << "nth ugly number: " << ugly_num << endl;
 
  return 0;
-}
+}