2025-05-17提交

77.combinations.java

@@ -0,0 +1,36 @@
+/*
+ * @lc app=leetcode id=77 lang=java
+ *
+ * [77] Combinations
+ */
+
+// @lc code=start
+class Solution {
+    public List<List<Integer>> combine(int n, int k) {
+        List<List<Integer>> r = new ArrayList<List<Integer>>();
+        List<Integer> rt = new ArrayList<Integer>();
+        dfsIterate(r,rt, 1, n, k);
+        return r;
+    }
+
+    private void dfsIterate(List<List<Integer>> r, List<Integer> list, int c, int n, int k) {
+        if(list.size() == k) {
+            r.add(shallowCopy(list));
+            return;
+        }
+        if(c > n) {
+            return;
+        }
+        for(int i = c; i<=n; i++) {
+            List<Integer> p = shallowCopy(list);
+            p.add(i);
+            dfsIterate(r, p, i+1, n, k);
+        }
+    }
+
+    private List<Integer> shallowCopy(List<Integer> list) {
+        return new ArrayList<>(list);
+    }
+}
+// @lc code=end
+