feat(csharp/backtracking): add subset_sum_i, _ii, _i_naive (#567)

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/**
* File: subset_sum_i.cs
* Created Time: 2023-06-25
* Author: hpstory (hpstory1024@163.com)
*/
namespace hello_algo.chapter_backtracking;
public class subset_sum_i {
/* 回溯算法:子集和 I */
public static void backtrack(List<int> state, int target, int[] choices, int start, List<List<int>> res) {
// 子集和等于 target 时,记录解
if (target == 0) {
res.Add(new List<int>(state));
return;
}
// 遍历所有选择
// 剪枝二:从 start 开始遍历,避免生成重复子集
for (int i = start; i < choices.Length; i++) {
// 剪枝一:若子集和超过 target ,则直接结束循环
// 这是因为数组已排序,后边元素更大,子集和一定超过 target
if (target - choices[i] < 0) {
break;
}
// 尝试:做出选择,更新 target, start
state.Add(choices[i]);
// 进行下一轮选择
backtrack(state, target - choices[i], choices, i, res);
// 回退:撤销选择,恢复到之前的状态
state.RemoveAt(state.Count - 1);
}
}
/* 求解子集和 I */
public static List<List<int>> subsetSumI(int[] nums, int target) {
List<int> state = new List<int>(); // 状态(子集)
Array.Sort(nums); // 对 nums 进行排序
int start = 0; // 遍历起始点
List<List<int>> res = new List<List<int>>(); // 结果列表(子集列表)
backtrack(state, target, nums, start, res);
return res;
}
[Test]
public void Test() {
int[] nums = { 3, 4, 5 };
int target = 9;
List<List<int>> res = subsetSumI(nums, target);
Console.WriteLine("输入数组 nums = " + string.Join(", ", nums) + ", target = " + target);
Console.WriteLine("所有和等于 " + target + " 的子集 res = ");
foreach (var subset in res) {
PrintUtil.PrintList(subset);
}
}
}

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/**
* File: subset_sum_i_naive.cs
* Created Time: 2023-06-25
* Author: hpstory (hpstory1024@163.com)
*/
namespace hello_algo.chapter_backtracking;
public class subset_sum_i_naive {
/* 回溯算法:子集和 I */
public static void backtrack(List<int> state, int target, int total, int[] choices, List<List<int>> res) {
// 子集和等于 target 时,记录解
if (total == target) {
res.Add(new List<int>(state));
return;
}
// 遍历所有选择
for (int i = 0; i < choices.Length; i++) {
// 剪枝:若子集和超过 target ,则跳过该选择
if (total + choices[i] > target) {
continue;
}
// 尝试:做出选择,更新元素和 total
state.Add(choices[i]);
// 进行下一轮选择
backtrack(state, target, total + choices[i], choices, res);
// 回退:撤销选择,恢复到之前的状态
state.RemoveAt(state.Count - 1);
}
}
/* 求解子集和 I包含重复子集 */
public static List<List<int>> subsetSumINaive(int[] nums, int target) {
List<int> state = new List<int>(); // 状态(子集)
int total = 0; // 子集和
List<List<int>> res = new List<List<int>>(); // 结果列表(子集列表)
backtrack(state, target, total, nums, res);
return res;
}
[Test]
public void Test() {
int[] nums = { 3, 4, 5 };
int target = 9;
List<List<int>> res = subsetSumINaive(nums, target);
Console.WriteLine("输入数组 nums = " + string.Join(", ", nums) + ", target = " + target);
Console.WriteLine("所有和等于 " + target + " 的子集 res = ");
foreach (var subset in res) {
PrintUtil.PrintList(subset);
}
Console.WriteLine("请注意,该方法输出的结果包含重复集合");
}
}

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/**
* File: subset_sum_ii.cs
* Created Time: 2023-06-25
* Author: hpstory (hpstory1024@163.com)
*/
namespace hello_algo.chapter_backtracking;
public class subset_sum_ii {
/* 回溯算法:子集和 II */
public static void backtrack(List<int> state, int target, int[] choices, int start, List<List<int>> res) {
// 子集和等于 target 时,记录解
if (target == 0) {
res.Add(new List<int>(state));
return;
}
// 遍历所有选择
// 剪枝二:从 start 开始遍历,避免生成重复子集
// 剪枝三:从 start 开始遍历,避免重复选择同一元素
for (int i = start; i < choices.Length; i++) {
// 剪枝一:若子集和超过 target ,则直接结束循环
// 这是因为数组已排序,后边元素更大,子集和一定超过 target
if (target - choices[i] < 0) {
break;
}
// 剪枝四:如果该元素与左边元素相等,说明该搜索分支重复,直接跳过
if (i > start && choices[i] == choices[i - 1]) {
continue;
}
// 尝试:做出选择,更新 target, start
state.Add(choices[i]);
// 进行下一轮选择
backtrack(state, target - choices[i], choices, i + 1, res);
// 回退:撤销选择,恢复到之前的状态
state.RemoveAt(state.Count - 1);
}
}
/* 求解子集和 II */
public static List<List<int>> subsetSumII(int[] nums, int target) {
List<int> state = new List<int>(); // 状态(子集)
Array.Sort(nums); // 对 nums 进行排序
int start = 0; // 遍历起始点
List<List<int>> res = new List<List<int>>(); // 结果列表(子集列表)
backtrack(state, target, nums, start, res);
return res;
}
[Test]
public void Test() {
int[] nums = { 4, 4, 5 };
int target = 9;
List<List<int>> res = subsetSumII(nums, target);
Console.WriteLine("输入数组 nums = " + string.Join(", ", nums) + ", target = " + target);
Console.WriteLine("所有和等于 " + target + " 的子集 res = ");
foreach (var subset in res) {
PrintUtil.PrintList(subset);
}
}
}