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| class Solution {
public List<List<String>> solveNQueens(int n) {
List<List<String>> list = new ArrayList<>();
char[][] board = new char[n][n];
for (int i = 0; i < n; i++) {
Arrays.fill(board[i], '.');
}
backtrack(list, board, 0);
return list;
}
private void backtrack(List<List<String>> list, char[][] board, int rowIndex) {
if (rowIndex == board.length) {
List<String> rowList = new ArrayList<>(board.length);
for (char[] line : board) {
rowList.add(new String(line));
}
list.add(rowList);
return;
}
for (int j = 0; j < board.length; j++) {
if (canFill(board, rowIndex, j)) {
board[rowIndex][j] = 'Q';
backtrack(list, board, rowIndex + 1);
board[rowIndex][j] = '.';
}
}
}
private boolean canFill(char[][] used, int i, int j) {
for (int k = 0; k < i; k++) {
if (used[k][j] == 'Q') {
return false;
}
}
for (int x = i - 1, y = j - 1; x >= 0 && y >= 0; x--, y--) {
if (used[x][y] == 'Q') {
return false;
}
}
for (int x = i - 1, y = j + 1; x >= 0 && y < used.length; x--, y++) {
if (used[x][y] == 'Q') {
return false;
}
}
return true;
}
}
|