Untitled

<!DOCTYPE html>
<html lang="ja">
  <head>
    <meta charset="utf-8">
    <title>8クイーン問題</title>
    <style>
      body {
          background: #eeeeee;
      }
      div {
          background: #ffffff;
          width: 400px;
          padding: 10px;
          text-align: center;
          margin: 30px auto;
      }
      table {
          margin-left:auto;
          margin-right:auto;
      }
      td {
          width: 40px;
          height: 40px;
          text-align: center;
          border: 1px solid #cccccc;
      }
    </style>
  </head>
  <body>
    <div>
      <h1>8クイーン問題</h1>
      <table id="board">
      </table>
    </div>

    <script type="text/javascript">
      function createBoard(table) {
          for (let i = 0; i < N; i++) {
              let row = table.insertRow(-1);
              for (let j = 0; j < N; j++) {
                  let cell = row.insertCell(-1);
              }
          }
      }

      function putQueen(table, row, col) {
          table.rows[row].cells[col].textContent = 'Q';
      }

      function removeQueen(table, row, col) {
          table.rows[row].cells[col].textContent = '';
      }

      function search(table, i) {
          for (let k = 0; k < N; k++) {
              if (col[k] === FREE && upwd[i+k] === FREE
                  && downwd[i-k+(N-1)] === FREE) {
                  putQueen(table, i, k);
                  col[k] = NOT_FREE;
                  upwd[i+k] = NOT_FREE;
                  downwd[i-k+(N-1)] = NOT_FREE;
                  if (i == N-1) {
                      return SUCCESS;
                  }
                  else {
                      if (search(table, i+1) == SUCCESS) {
                          return SUCCESS;
                      }
                      else {
                          removeQueen(table, i, k);
                          col[k] = FREE;
                          upwd[i+k] = FREE;
                          downwd[i-k+(N-1)] = FREE;
                      }
                  }
              }
          }
          return FAILURE;
      }

      // Main
      const N = 8;
      const FREE = 0;
      const NOT_FREE = 1;
      const SUCCESS = 0;
      const FAILURE = 1;

      let table = document.getElementById('board');
      createBoard(table);
      let col = [];
      for (let i = 0; i < N; i++) {
          col.push(FREE);
      }
      let upwd = []
      let downwd = [];
      for (let i = 0; i < 2*N-1; i++) {
          upwd.push(FREE); downwd.push(FREE);
      }
      search(table, 0);
    </script>
  </body>
</html>