Random Country Selection By Popluation

https://github.com/mission-peace/interview/blob/master/src/com/interview/random/RandomCountrySelectionByPopluation.java
public int getRandom(int []arr){
  int sum[] = new int[arr.length];
  sum[0] = arr[0];
  int n = arr[0];
  for(int i=1; i < sum.length; i++){
    sum[i] = sum[i-1] + arr[i];
    n += arr[i];
  }

  int ran = (int)(Math.random()*n + 1);

  int low = 0;
  int high = arr.length-1;
  int mid = (high + low)/2;
  while(true){
    if(sum[mid] >= ran && (mid-1 == -1 || sum[mid-1] < ran)){
      break;
    }
    if(sum[mid] > ran){
      high = mid-1;
    }else{
      low = mid+1;
    }
    mid = (high + low)/2;
  }
  return mid;
}

  RandomCountrySelectionByPopluation rcsp = new RandomCountrySelectionByPopluation();
  int arr[] = {5,5,2,3,7,1};
  for(int i=0; i < 10; i++){
    System.out.print(rcsp.getRandom(arr));
  }

https://github.com/mission-peace/interview/blob/master/src/com/interview/random/SelectMRandomNumbersInStream.java
public int[] selectRandom(int arr[],int m){
  int result[] = new int[m];
  for(int i=0; i < m ;i++){
    result[i] = arr[i];
  }

  for(int i=m ; i < arr.length; i++){
    int random = (int)(Math.random()*i) + 1;
    if(random <= m){
      result[random-1] = arr[i];
    }
  }
  return result;
}

https://github.com/mission-peace/interview/blob/master/src/com/interview/random/ShuffleArray.java

public void shuffle(int arr[]){

  for(int i=arr.length-1; i>=0; i--){

    int random = (int)(Math.random()*(i+1)) ;

    System.out.print(random +  " ");

    swap(arr,random,i);

  }

}

https://github.com/mission-peace/interview/blob/master/src/com/interview/random/Rand7UsingRand5.java

public int rand7(){

  int r = (rand5()-1)*5 + rand5();

  while(r > 21){   // I just need to ignore [22, 25] 

    r = (rand5()-1)*5 + rand5();

  }

  return (r%7) + 1;

}

private int rand5(){

  return (int)(Math.ceil(Math.random()*5));

}

int rand7 () {
    while (true) {
            int num = 5 * randS() + randS();
            if (num < 21) {
                    return num % 7;
            }
    }
}
int rand7() {
  while (true) {
    int rl = 2* rands(); /* evens between 0 and 9 */
    int r2 = rand5(); /*used later to generate a·0 or 1 */
    if (r2 != 4) {
            /* r2 has extra even num-discard the extra* /
      int randl = r2 % 2; /*Ge nerate 0 or 1 */
      int num = rl + randl; /* will be in the range 0 to 9 */
      if (num < 7) {
        return num;
      }
  }
}