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# Alien Invasion CodeChef Solution

## Alien Invasion CodeChef Solution in C++17

``````#include <bits/stdc++.h>
using namespace std;
#define ll long long

double m, mid, l, r, k, ans, temp, cd;
int n, t, d;
int a[200001];
bool check(double c) {
cd = 0;
for (int i = 1; i <= n; i++) {
if (cd > a[i] + d) {
return false;
} else if (cd < a[i]) {
cd = a[i] + c;
} else {
cd = cd + c;
}
}
return true;
}

int main() {
cin >> t;
for (int h = 1; h <= t; h++) {
cin >> n >> d;
for (int i = 1; i <= n; i++) {
cin >> a[i];
}
sort(a + 1, a + n + 1);
r = 2e9;
l = 0;
temp = 0;
for (int i = 1; i <= 101; i++) {
mid = (l+r)/2;
if (check(mid) == true) {
temp = mid;
l = mid;
} else {
r = mid;
}
}
cout << fixed << setprecision(10) << temp << endl;
}
}``````

## Alien Invasion CodeChef Solution in C++14

``````#ifndef ONLINE_JUDGE
#include "debug.h"
#else
#include <bits/stdc++.h>
using namespace std;
#endif
#define int long long int

int n,d;
double v[100001];

bool f(double t)
{
double curr=v[0]+t;
int i;
for(i=1;i<n;i++)
{
if(v[i]+d>=curr)
{
curr=max(curr,v[i]);
curr+=t;
}
else
break;
}
return (i==n);
}

void solve()
{
cin>>n>>d;
for(int i=0;i<n;i++)
cin>>v[i];
sort(v,v+n);
double l=0,r=1e10;
while(r-l>1e-6)
{
double mid=(l+r)/2;
if(f(mid))
l=mid;
else
r=mid;
}
cout<<fixed<<setprecision(6)<<l<<'\n';
}
int32_t main()
{
#ifndef ONLINE_JUDGE
freopen("input.txt","r",stdin);
freopen("Error.txt","w",stderr);
freopen("output.txt","w",stdout);
#endif
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t=1;
cin>>t;
while(t--)
solve();
return 0;
}``````

## Alien Invasion CodeChef Solution in C

``````//set many funcs template
//Ver.20190820
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<stdbool.h>
#include<time.h>
#include<assert.h>
#define inf 1072114514
#define llinf 4154118101919364364
#define mod 1000000007
#define pi 3.1415926535897932384

int max(int a,int b){if(a>b){return a;}return b;}
int min(int a,int b){if(a<b){return a;}return b;}
int zt(int a,int b){return max(a,b)-min(a,b);}
int round(int a,int b){if((a%b)*2 >= b){return (a/b)+1;}return a/b;}
int ceil(int a,int b){if(a%b==0){return a/b;}return (a/b)+1;}
int gcd(int a,int b){int c;while(b!=0){c=a%b;a=b;b=c;}return a;}
int lcm(int a,int b){int c=gcd(a,b);a/=c;return a*b;}
int nCr(int a,int b){int i,r=1;for(i=1;i<=b;i++){r*=(a+1-i);r/=i;}return r;}
int nHr(int a,int b){return nCr(a+b-1,b);}
int fact(int a){int i,r=1;for(i=1;i<=a;i++){r*=i;}return r;}
int pow(int a,int b){int i,r=1;for(i=1;i<=b;i++){r*=a;}return r;}
int dsum(int x){int r=0;while(x){r+=(x%10);x/=10;}return r;}
int dsumb(int x,int b){int r=0;while(x){r+=(x%b);x/=b;}return r;}
int sankaku(int x){return ((1+x)*x)/2;}
void swap(int *a,int *b){int c;c=(*a);(*a)=(*b);(*b)=c;}
long long llmax(long long a,long long b){if(a>b){return a;}return b;}
long long llmin(long long a,long long b){if(a<b){return a;}return b;}
long long llzt(long long a,long long b){return llmax(a,b)-llmin(a,b);}
long long llround(long long a,long long b){if((a%b)*2 >= b){return (a/b)+1;}return a/b;}
long long llceil(long long a,long long b){if(a%b==0){return a/b;}return (a/b)+1;}
long long llgcd(long long a,long long b){long long c;while(b!=0){c=a%b;a=b;b=c;}return a;}
long long lllcm(long long a,long long b){long long c=llgcd(a,b);a/=c;return a*b;}
long long llnCr(long long a,long long b){long long i,r=1;for(i=1;i<=b;i++){r*=(a+1-i);r/=i;}return r;}
long long llnHr(long long a,long long b){return llnCr(a+b-1,b);}
long long llfact(long long a){long long i,r=1;for(i=1;i<=a;i++){r*=i;}return r;}
long long llpow(long long a,long long b){long long i,r=1;for(i=1;i<=b;i++){r*=a;}return r;}
long long lldsum(long long x){long long r=0;while(x){r+=(x%10);x/=10;}return r;}
long long lldsumb(long long x,long long b){long long r=0;while(x){r+=(x%b);x/=b;}return r;}
long long llsankaku(long long x){return ((1+x)*x)/2;}
void llswap(long long *a,long long *b){long long c;c=(*a);(*a)=(*b);(*b)=c;}
double dbmax(double a,double b){if(a>b){return a;}return b;}
double dbmin(double a,double b){if(a<b){return a;}return b;}
double dbzt(double a,double b){return dbmax(a,b)-dbmin(a,b);}
void dbswap(double *a,double *b){double c;c=(*a);(*a)=(*b);(*b)=c;}
void chswap(char *a,char *b){char c;c=(*a);(*a)=(*b);(*b)=c;}
int sortfncsj(const void *a,const void *b){if(*(int *)a>*(int *)b){return 1;}if(*(int *)a==*(int *)b){return 0;}return -1;}
int sortfnckj(const void *a,const void *b){if(*(int *)a<*(int *)b){return 1;}if(*(int *)a==*(int *)b){return 0;}return -1;}
int llsortfncsj(const void *a,const void *b){if(*(long long *)a>*(long long *)b){return 1;}if(*(long long *)a==*(long long *)b){return 0;}return -1;}
int llsortfnckj(const void *a,const void *b){if(*(long long *)a<*(long long *)b){return 1;}if(*(long long *)a==*(long long *)b){return 0;}return -1;}
int dbsortfncsj(const void *a,const void *b){if(*(double *)a>*(double *)b){return 1;}if(*(double *)a==*(double *)b){return 0;}return -1;}
int dbsortfnckj(const void *a,const void *b){if(*(double *)a<*(double *)b){return 1;}if(*(double *)a==*(double *)b){return 0;}return -1;}
int strsortfncsj(const void *a,const void *b){return strcmp((char *)a,(char *)b);}
int strsortfnckj(const void *a,const void *b){return strcmp((char *)b,(char *)a);}
int chsortfncsj(const void *a,const void *b){if(*(char *)a>*(char *)b){return 1;}if(*(char *)a==*(char *)b){return 0;}return -1;}
int chsortfnckj(const void *a,const void *b){if(*(char *)a<*(char *)b){return 1;}if(*(char *)a==*(char *)b){return 0;}return -1;}

void shuffledget(int x[],int n){
int i,b[524288],p,c;
for(i=0;i<n;i++){
b[i]=i;
}
for(i=n;i>=1;i--){
p=rand()%i;
c=b[i-1];b[i-1]=b[p];b[p]=c;
}
for(i=0;i<n;i++){
scanf("%d",&x[b[i]]);
}
}

int dx4[4]={1,-1,0,0};
int dy4[4]={0,0,1,-1};
int dx8[8]={-1,-1,-1,0,0,1,1,1};
int dy8[8]={-1,0,1,-1,1,-1,0,1};

int search(int x,int a[],int n){
int st=0,fi=n-1,te;
while(st<=fi){
te=(st+fi)/2;
if(a[te]<x){st=te+1;}else{fi=te-1;}
}
return st;
}

void prarr(int arr[],int n){
int i;
for(i=0;i<n;i++){
if(i){printf(" ");}
printf("%d",arr[i]);
}
printf("\n");
return;
}

void getperm(int a[],int n){
int i,p;
for(i=0;i<n;i++){
a[i]=i;
}
for(i=n-1;i>=1;i--){
p=rand()%(i+1);
swap(&a[p],&a[i]);
}
}

typedef struct{
int val;
int node;
}sd;

int sdsortfnc(const void *a,const void *b){
if(((sd*)a)->val < ((sd*)b)->val){return -1;}
if(((sd*)a)->val > ((sd*)b)->val){return 1;}
return 0;
}

void coordinate_comp(int a[],int n){
int i,c=0;
sd dat[524288];
for(i=0;i<n;i++){
dat[i].val=a[i];
dat[i].node=i;
}
qsort(dat,n,sizeof(dat[0]),sdsortfnc);
a[dat[0].node]=c;
for(i=1;i<n;i++){
if(dat[i-1].val!=dat[i].val){c++;}
a[dat[i].node]=c;
}
}

int main(void){
int n,i,j,t;
double d,a[524288],st,fi,te,cl;
scanf("%d",&t);
while(t>0){
t--;
scanf("%d%lf",&n,&d);
for(i=0;i<n;i++){scanf("%lf",&a[i]);}
qsort(a,n,sizeof(double),dbsortfncsj);
st=0;fi=3.0e9;
for(i=0;i<200;i++){
te=(st+fi)/2.0;
cl=-3.0e9;
for(j=0;j<n;j++){
cl=dbmax(a[j],cl+te);
if(cl>a[j]+d){fi=te;break;}
if(j==n-1){st=te;}
}
}
printf("%.12lf\n",fi);
}
return 0;
}``````

## Alien Invasion CodeChef Solution in JAVA

``````import java.util.*;

class Main {

public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int t = input.nextInt();
while(t-- > 0) {
int n = input.nextInt(), d = input.nextInt();
int[] arr = new int[n];
for (int i = 0; i < n; i++) {
arr[i] = input.nextInt();
}
Arrays.sort(arr);
double low = 0, high = 2e9;
while (low + 1e-6 <= high) {
double mid = 0.5 * (low + high);
if (isvalid(arr, d, mid, n)) {
low = mid;
} else {
high = mid;
}
}
System.out.println(low);
}
input.close();
}
private static boolean isvalid(int[] arr, int d, double mid, int n) {
double kill = 0.0;
for (int i = 0; i < n; i++) {
if (kill <= arr[i] + d) {
kill = Math.max(arr[i] + mid, kill + mid);
} else {
return false;
}
}
return true;
}
}``````

## Alien Invasion CodeChef Solution in PYPY 3

``````from sys import stdin

def check(x):

cooldown = 0
for i in range(n):
if(cooldown > (c[i] + d)):return False
cooldown = max(cooldown , c[i]) + x

return True

l , r = 0 , 10**10

for i in range(101):

mid = (l + r)/2

if(check(mid)):
l = mid
ans = mid
else:
r = mid

return ans

for T in range(int(input())):

n , d = map(int,input().split())

c = sorted(list(map(int,input().split())))

## Alien Invasion CodeChef Solution in GO

``````package main

import (
"bufio"
"fmt"
"math"
"os"
"sort"
)

func main() {

for tc > 0 {
tc--
res := solve(n, D, C)
fmt.Printf("%.7f\n", res)
}
}

func readInt(bytes []byte, from int, val *int) int {
i := from
sign := 1
if bytes[i] == '-' {
sign = -1
i++
}
tmp := 0
for i < len(bytes) && bytes[i] >= '0' && bytes[i] <= '9' {
tmp = tmp*10 + int(bytes[i]-'0')
i++
}
*val = tmp * sign
return i
}

return
}

a, b = res[0], res[1]
return
}

a, b, c = res[0], res[1], res[2]
return
}

res := make([]int, n)
x := 0
for i := 0; i < n; i++ {
for x < len(bs) && (bs[x] < '0' || bs[x] > '9') && bs[x] != '-' {
x++
}
}
return res
}

func readUint64(bytes []byte, from int, val *uint64) int {
i := from

var tmp uint64
for i < len(bytes) && bytes[i] >= '0' && bytes[i] <= '9' {
tmp = tmp*10 + uint64(bytes[i]-'0')
i++
}
*val = tmp

return i
}

func solve(n int, D int, C []int) float64 {
sort.Ints(C)

check := func(cooldown float64) bool {
var canFireAt float64

for i := 0; i < n; i++ {
a := float64(C[i])
b := float64(C[i] + D)

if canFireAt > b {
return false
}
canFireAt = math.Max(a, canFireAt) + cooldown
}
return true
}

var left, right float64 = 0, float64(int64(1) << 33)

for i := 0; i < 60; i++ {
mid := (left + right) / 2
if check(mid) {
left = mid
} else {
right = mid
}
}
return (left + right) / 2
}``````
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