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754. Reach a Number

  • Time: $O(\sqrt{\texttt{target}})$
  • Space: $O(1)$
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class Solution {
 public:
  int reachNumber(int target) {
    const int newTarget = abs(target);
    int ans = 0;
    int pos = 0;

    while (pos < newTarget)
      pos += ++ans;
    while ((pos - newTarget) % 2 == 1)
      pos += ++ans;

    return ans;
  }
};

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class Solution {
  public int reachNumber(int target) {
    final int newTarget = Math.abs(target);
    int ans = 0;
    int pos = 0;

    while (pos < newTarget)
      pos += ++ans;
    while ((pos - newTarget) % 2 == 1)
      pos += ++ans;

    return ans;
  }
}

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class Solution:
  def reachNumber(self, target: int) -> int:
    ans = 0
    pos = 0
    target = abs(target)

    while pos < target:
      ans += 1
      pos += ans

    while (pos - target) % 2 == 1:
      ans += 1
      pos += ans

    return ans