77. 组合-蒲公英云

77. 组合

怼烎@ 2023-10-04 08:31 28阅读 0赞

给定两个整数 n 和 k，返回 1 … n 中所有可能的 k 个数的组合。

示例:

输入: n = 4, k = 2
输出:
[
  [2,4],
  [3,4],
  [2,3],
  [1,2],
  [1,3],
  [1,4],
]
package Solution77;
import java.util.ArrayList;
import java.util.List;
class Solution5 {
    public List<List<Integer>> combine(int n, int k) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        int elements[] = new int[n];
        for (int i = 0; i < n; i++) {
            elements[i] = i + 1;
        }
        for (int i = 0; i < (1 << n); i++) {
            if (Integer.bitCount(i) == k) {
                ArrayList<Integer> temp = new ArrayList<Integer>();
                for (int j = 0; j < n; j++) {
                    if ((i & (1 << j)) > 0) {
                        temp.add(elements[j]);
                    }
                }
                result.add(temp);
            }
        }
        return result;
    }
    public static void main(String[] args) {
        Solution5 sol = new Solution5();
        int n = 4;
        int k = 2;
        System.out.println(sol.combine(n, k));
    }
}

watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2FsbHdheTI_size_16_color_FFFFFF_t_70

继续优化

package Solution77;
import java.util.ArrayList;
import java.util.List;
class Solution8 {
    public List<List<Integer>> combine(int n, int k) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        for (int i = 0; i < (1 << n); i++) {
            if (Integer.bitCount(i) == k) {
                ArrayList<Integer> temp = new ArrayList<Integer>();
                for (int j = 0; j < n; j++) {
                    if ((i & (1 << j)) > 0) {
                        temp.add(j + 1);
                    }
                }
                result.add(temp);
            }
        }
        return result;
    }
    public static void main(String[] args) {
        Solution8 sol = new Solution8();
        int n = 4;
        int k = 2;
        System.out.println(sol.combine(n, k));
    }
}