feat: add solutions to lc problem: No.0216

No.0216.Combination Sum III

Author: yanglbme

solution/0200-0299/0216.Combination Sum III/README.md

@@ -1,23 +1,24 @@
 class Solution {
 public:
-    vector<vector<int>> ans;
-
     vector<vector<int>> combinationSum3(int k, int n) {
+        vector<vector<int>> ans;
         vector<int> t;
-        dfs(0, n, k, t);
+        function<void(int, int)> dfs = [&](int i, int s) {
+            if (s == 0) {
+                if (t.size() == k) {
+                    ans.emplace_back(t);
+                }
+                return;
+            }
+            if (i > 9 || i > s || t.size() >= k) {
+                return;
+            }
+            t.emplace_back(i);
+            dfs(i + 1, s - i);
+            t.pop_back();
+            dfs(i + 1, s);
+        };
+        dfs(1, n);
         return ans;
     }
-
-    void dfs(int i, int n, int k, vector<int>& t) {
-        if (i > 9 || n < 0 || t.size() > k) return;
-        if (n == 0 && t.size() == k) {
-            ans.push_back(t);
-            return;
-        }
-        ++i;
-        t.push_back(i);
-        dfs(i, n - i, k, t);
-        t.pop_back();
-        dfs(i, n, k, t);
-    }
 };

solution/0200-0299/0216.Combination Sum III/README_EN.md

@@ -1,59 +1,27 @@
-using System.Collections.Generic;
+public class Solution {
+    private List<IList<int>> ans = new List<IList<int>>();
+    private List<int> t = new List<int>();
+    private int k;
 
-public class Solution
-{
-    public IList<IList<int>> CombinationSum3(int k, int n)
-    {
-        if (n == 0 || k == 0) return new IList<int>[0];
-
-        var paths = new List<int>[n + 1, k + 1];
-        paths[0, 0] = new List<int>();
-        for (var c = 1; c <= 9; ++c)
-        {
-            for (var j = n; j >= c; --j)
-            {
-                for (var kk = 1; kk <= k; ++kk)
-                {
-                    if (paths[j - c, kk - 1] != null)
-                    {
-                        if (paths[j, kk] == null)
-                        {
-                            paths[j, kk] = new List<int>();
-                        }
-                        paths[j, kk].Add(c);
-                    }
-                }
-            }
-        }
-
-        var results = new List<IList<int>>();
-        if (paths[n, k] != null && paths[n, k].Count > 0) GenerateResults(results, new Stack<int>(), paths, k, n, paths[n, k].Count - 1);
-        return results;
+    public IList<IList<int>> CombinationSum3(int k, int n) {
+        this.k = k;
+        dfs(1, n);
+        return ans;
     }
 
-    private void GenerateResults(IList<IList<int>> results, Stack<int> result, List<int>[,] paths, int k, int n,
-        int maxIndex)
-    {
-        if (n == 0)
-        {
-            results.Add(new List<int>(result));
+    private void dfs(int i, int s) {
+        if (s == 0) {
+            if (t.Count == k) {
+                ans.Add(new List<int>(t));
+            }
             return;
         }
-        for (var i = maxIndex; i >= 0; --i)
-        {
-            var value = paths[n, k][i];
-            result.Push(value);
-            var nextMaxIndex = paths[n - value, k - 1].BinarySearch(value);
-            if (nextMaxIndex >= 0)
-            {
-                --nextMaxIndex;
-            }
-            else if (nextMaxIndex < 0)
-            {
-                nextMaxIndex = ~nextMaxIndex - 1;
-            }
-            GenerateResults(results, result, paths, k - 1, n - value, nextMaxIndex);
-            result.Pop();
+        if (i > 9 || i > s || t.Count >= k) {
+            return;
         }
+        t.Add(i);
+        dfs(i + 1, s - i);
+        t.RemoveAt(t.Count - 1);
+        dfs(i + 1, s);
     }
 }

solution/0200-0299/0216.Combination Sum III/Solution.cpp

@@ -1,24 +1,23 @@
-func combinationSum3(k int, n int) [][]int {
-	var ans [][]int
-	var t []int
-	var dfs func(i, n int, t []int)
-	dfs = func(i, n int, t []int) {
-		if i > 9 || n < 0 || len(t) > k {
+func combinationSum3(k int, n int) (ans [][]int) {
+	t := []int{}
+	var dfs func(i, s int)
+	dfs = func(i, s int) {
+		if s == 0 {
+			if len(t) == k {
+				cp := make([]int, len(t))
+				copy(cp, t)
+				ans = append(ans, cp)
+			}
 			return
 		}
-		if n == 0 && len(t) == k {
-			cp := make([]int, len(t))
-			copy(cp, t)
-			ans = append(ans, cp)
+		if i > 9 || i > s || len(t) >= k {
 			return
 		}
-		i++
 		t = append(t, i)
-		dfs(i, n-i, t)
+		dfs(i+1, s-i)
 		t = t[:len(t)-1]
-		dfs(i, n, t)
+		dfs(i+1, s)
 	}
-
-	dfs(0, n, t)
-	return ans
+	dfs(1, n)
+	return
 }

solution/0200-0299/0216.Combination Sum III/Solution.cs

@@ -1,24 +1,27 @@
 class Solution {
-    private List<List<Integer>> ans;
+    private List<List<Integer>> ans = new ArrayList<>();
+    private List<Integer> t = new ArrayList<>();
+    private int k;
 
     public List<List<Integer>> combinationSum3(int k, int n) {
-        ans = new ArrayList<>();
-        dfs(0, n, k, new ArrayList<>());
+        this.k = k;
+        dfs(1, n);
         return ans;
     }
 
-    private void dfs(int i, int n, int k, List<Integer> t) {
-        if (i > 9 || n < 0 || t.size() > k) {
+    private void dfs(int i, int s) {
+        if (s == 0) {
+            if (t.size() == k) {
+                ans.add(new ArrayList<>(t));
+            }
             return;
         }
-        if (n == 0 && t.size() == k) {
-            ans.add(new ArrayList<>(t));
+        if (i > 9 || i > s || t.size() >= k) {
             return;
         }
-        ++i;
         t.add(i);
-        dfs(i, n - i, k, t);
+        dfs(i + 1, s - i);
         t.remove(t.size() - 1);
-        dfs(i, n, k, t);
+        dfs(i + 1, s);
     }
 }

solution/0200-0299/0216.Combination Sum III/Solution.go

@@ -1,17 +1,18 @@
 class Solution:
     def combinationSum3(self, k: int, n: int) -> List[List[int]]:
-        def dfs(i, s, t):
-            if i > 9 or s > n or len(t) > k:
+        def dfs(i: int, s: int):
+            if s == 0:
+                if len(t) == k:
+                    ans.append(t[:])
                 return
-            if s == n and len(t) == k:
-                ans.append(t[:])
+            if i > 9 or i > s or len(t) >= k:
                 return
-            i += 1
             t.append(i)
-            dfs(i, s + i, t)
+            dfs(i + 1, s - i)
             t.pop()
-            dfs(i, s, t)
+            dfs(i + 1, s)
 
         ans = []
-        dfs(0, 0, [])
+        t = []
+        dfs(1, n)
         return ans

solution/0200-0299/0216.Combination Sum III/Solution.java

@@ -0,0 +1,21 @@
+function combinationSum3(k: number, n: number): number[][] {
+    const ans: number[][] = [];
+    const t: number[] = [];
+    const dfs = (i: number, s: number) => {
+        if (s === 0) {
+            if (t.length === k) {
+                ans.push(t.slice());
+            }
+            return;
+        }
+        if (i > 9 || i > s || t.length > k) {
+            return;
+        }
+        t.push(i);
+        dfs(i + 1, s - i);
+        t.pop();
+        dfs(i + 1, s);
+    };
+    dfs(1, n);
+    return ans;
+}