Today I have done leetcode's January LeetCoding Challenge with cpp.

January LeetCoding Challenge 22

Description

Stone Game IV

Alice and Bob take turns playing a game, with Alice starting first.

Initially, there are n stones in a pile. On each player's turn, that player makes a move consisting of removing any non-zero square number of stones in the pile.

Also, if a player cannot make a move, he/she loses the game.

Given a positive integer n, return true if and only if Alice wins the game otherwise return false, assuming both players play optimally.

Example 1:

Input: n = 1
Output: true
Explanation: Alice can remove 1 stone winning the game because Bob doesn't have any moves.

Example 2:

Input: n = 2
Output: false
Explanation: Alice can only remove 1 stone, after that Bob removes the last one winning the game (2 -> 1 -> 0).

Example 3:

Input: n = 4
Output: true
Explanation: n is already a perfect square, Alice can win with one move, removing 4 stones (4 -> 0).

Constraints:

• 1 <= n <= 10^5

Solution

constexpr int LIMIT = 100000;
auto table = [](){
  array<bool, LIMIT + 1> arr{false};
  for(int i = 0; i <= LIMIT; ++i) {
    if(arr[i]) continue;
    for(int j = 1; j * j + i <= LIMIT; ++j) {
      arr[i + j * j] = true;
    }
  }
  return arr;
}();
class Solution {
public:
  bool winnerSquareGame(int n) {
    return table[n];
  }
};

// Accepted
// 72/72 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 93.92 % of cpp submissions (6 MB)