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LeetCode :My solution N-Queens
N-Queens
Total Accepted: 15603 Total Submissions: 60198My SubmissionsThe n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.
Given an integer n, return all distinct solutions to the n-queens puzzle.
Each solution contains a distinct board configuration of the n-queens‘ placement, where ‘Q‘ and ‘.‘ both indicate a queen and an empty space respectively.
For example,
There exist two distinct solutions to the 4-queens puzzle:
[ [".Q..", // Solution 1 "...Q", "Q...", "..Q."], ["..Q.", // Solution 2 "Q...", "...Q", ".Q.."] ]
public class Solution {
public List<String[]> solveNQueens(int n) {
List<String[]> result = new ArrayList<String[]>();
if ( n < 1) {
return result ;
}
List<List<Integer>> storeArray = new ArrayList<List<Integer>>();
helper(n, new ArrayList<Integer>(), storeArray);
result = drawPicture(storeArray,n);
return result;
}
private List<String[]> drawPicture(List<List<Integer>> storeArray ,int n) {
List<String[]> drawedPicture = new ArrayList<String[]> ();
for (int i = 0; i < storeArray.size();i++) {
String[] str = new String[n];
for (int j = 0; j < n; j++) {
str[j] = new String("");
for (int w = 0; w < n; w++) {
if (storeArray.get(i).get(j) == w) {
str[j] +="Q";
} else {
str[j] +=".";
}
}
}
drawedPicture.add(str);
}
return drawedPicture;
}
boolean isValid(ArrayList<Integer> cols, int col) {
int newX = col;
int newY = cols.size();
for (int y = 0; y < cols.size(); y++) {
int x = cols.get(y);
if (newX == x) {
return false;
}
if (newX - newY == x - y) {
return false;
}
if (newX + newY == x + y){
return false;
}
}
return true;
}
public void helper(int n, ArrayList<Integer> cols, List<List<Integer>> storeArray) {
if (cols.size() == n) {
storeArray.add(new ArrayList<Integer>(cols));
return;
}
for (int i = 0; i < n; i++) {
if (!isValid(cols, i)) {
continue;
}
cols.add(i);
helper(n, cols, storeArray);
cols.remove(cols.size() - 1);
}
}
}LeetCode :My solution N-Queens
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