move-all-0s-to-left-while-maintaining-order.cpp

#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
#include <algorithm>
#include <bits/stdc++.h>
#include <chrono>
#include <cmath>
#include <complex>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> p32;
typedef pair<ll, ll> p64;
typedef pair<double, double> pdd;
typedef vector<ll> v64;
typedef vector<int> v32;
typedef vector<vector<int>> vv32;
typedef vector<vector<ll>> vv64;
typedef vector<vector<p64>> vvp64;
typedef vector<p64> vp64;
typedef vector<p32> vp32;
ll MOD = 998244353;
double eps = 1e-12;
#define forn(i, e) for (ll i = 0; i < e; i++)
#define forsn(i, s, e) for (ll i = s; i < e; i++)
#define rforn(i, s) for (ll i = s; i >= 0; i--)
#define rforsn(i, s, e) for (ll i = s; i >= e; i--)
#define ln "\n"
#define dbg(x) cout << #x << " = " << x << ln
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define INF 2e18
#define fast_cin()                                                             \
  ios_base::sync_with_stdio(false);                                            \
  cin.tie(NULL);                                                               \
  cout.tie(NULL)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())

void output(vector<int> arr) {
  int arrSize = arr.size();

  for (int i = 0; i < arrSize; ++i) {
    std::cout << arr[i] << '\t';
  }
  std::cout << std::endl;
}
void twoPointerTechnique(vector<int> *arr) {
  int r = arr->size() - 1, w = arr->size() - 1;
  while (r >= 0) {
      if(arr->at(r) ==0){
          r--;
      }else{
          swap(arr->at(w--),arr->at(r--));
      }
//     if (arr->at(r) != 0) {
//       arr->at(w) = arr->at(r);
//       w--;
//     }
//     r--;
//   }
//   while (w >= 0) {
//     arr->at(w) = 0;
//     w--;
  }
}
int main() {
  vector<int> a = {1, 0, 2, 0, 3, 0,0};

  output(a);
  twoPointerTechnique(&a);
  std::cout << "After" << std::endl;
  output(a);
}