2025-05-17提交

51.n-queens.java

@@ -0,0 +1,183 @@
+/*
+ * @lc app=leetcode id=51 lang=java
+ *
+ * [51] N-Queens
+ */
+
+// @lc code=start
+
+import java.util.ArrayList;
+
+class Solution {
+    public List<List<String>> solveNQueens(int n) {
+        int[][] m = createMap(n);
+        List<List<String>> r = new ArrayList<>();
+        dfsNQueen(r, m, 0, n, 0);
+        return r;
+    }
+
+    private void dfsNQueen(List<List<String>> r, int[][] m, int i, int n, int p) {
+        if(i == n && pass(m, n, i)) {
+            r.add(buildRetStr(m));
+            return;
+        } else if (i>=n) {
+            return;
+        }
+        if(!pass(m,n, i)) {
+            return;
+        }
+        for(int j = p; j<n*n; j++) {
+            int x = j / n;
+            int y = j % n;
+            if(m[x][y] == 0) {
+                m[x][y] = 1;
+                dfsNQueen(r, m, i+1, n, j+1);
+                m[x][y] = 0;
+            }
+        }
+    }
+
+    private boolean pass(int[][] m , int n, int i) {
+        // todo: check logic
+        return checkRow(m, n, i) && checkColumn(m, n) && checkLeftSlash(m,n) && checkRightSlash(m,n);
+    }
+
+    private boolean checkRow(int[][] m, int n, int s) {
+        for(int i=0; i<n; i++) {
+            if(!checkWithStrategy(m, new Point(i, 0), n, pos->{
+                return new Point(pos.x, pos.y+1);
+            })) {
+                return false;
+            }
+            if(i < s && !checkRowNotEmpty(m, n, i)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private boolean checkRowNotEmpty(int[][] m, int n, int s) {
+        for(int i=0; i<n; i++) {
+            if(m[s][i] != 0) {
+                return true;
+            }
+        }
+        return false;
+    }
+    
+    private boolean checkColumn(int[][] m, int n) {
+        for(int i = 0; i<n; i++) {
+            if(!checkWithStrategy(m, new Point(0, i), n, pos->{
+                return new Point(pos.x+1, pos.y);
+            })) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private boolean checkLeftSlash(int[][] m, int n) {
+        for(int i = 0; i<n; i++) {
+            if(!checkWithStrategy(m, new Point(i, 0), n, pos->{
+                return new Point(pos.x+1, pos.y+1);
+            })) {
+                return false;
+            }
+            if(!checkWithStrategy(m, new Point(0, i), n, pos->{
+                return new Point(pos.x+1, pos.y+1);
+            })) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private boolean checkRightSlash(int[][] m, int n) {
+        for(int i = 0; i<n; i++) {
+            if(!checkWithStrategy(m, new Point(0, i), n, pos->{
+                return new Point(pos.x+1, pos.y-1);
+            })) {
+                return false;
+            }
+            if(!checkWithStrategy(m, new Point(i, n-1), n, pos->{
+                return new Point(pos.x+1, pos.y-1);
+            })) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+
+    private boolean checkWithStrategy(int[][] m, Point pos, int n,Function<Point, Point> incrStrategy) {
+        int c = 0;
+        if(m[pos.x][pos.y] !=0) {
+            c++;
+        }
+        for(int i=0;i<n-1;i++) {
+            pos = incrStrategy.apply(pos);
+            if(pos.x >=n || pos.y>= n || pos.x <0 || pos.y <0) {
+                break;
+            }
+            if(m[pos.x][pos.y] != 0) {
+                c++;
+                if(c>1) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    private int[][] createMap(int n) {
+        int[][] r = new int[n][n];
+        zset(r);
+        return r;
+    }
+
+    private void zset(int[][] m) {
+        if(m == null) {
+            return;
+        }
+        for (int i = 0; i < m.length; i++) {
+            if(m[i]==null) {
+                continue;
+            }
+            for(int j = 0; j < m[i].length; j++) {
+                m[i][j] = 0;
+            }
+        }
+    }
+
+    private List<String> buildRetStr(int[][] m) {
+        List<String> r = new ArrayList<String>();
+        if(m == null) {
+            return r;
+        }
+        for(int i = 0; i<m.length; i++) {
+            int[] t = m[i];
+            if(t == null) {
+                r.add("");
+                continue;
+            }
+            StringBuilder sbd = new StringBuilder();
+            for(int j = 0; j<t.length; j++) {
+                sbd.append(t[j]==0?".":"Q");
+            }
+            r.add(sbd.toString());
+        }
+        return r;
+    }
+
+    public static class Point {
+        public int x;
+        public int y;
+
+        public Point(int x, int y) {
+            this.x = x;
+            this.y = y;
+        }
+    }
+}
+// @lc code=end
+