Update 39. 组合总和.md

Author: CompetitiveLin

Backtrace/39. 组合总和.md

@@ -44,7 +44,7 @@
 
 ---
 
-回溯 + 剪枝：
+**方法一：枚举选哪个**
 
 从 `target` 开始，每次回溯都减或不减当前下标的值。本题用到剪枝在于先将数组按升序排序，如果当前下标的值小于 `target` 了，那么后续也不需要遍历了。
 
@@ -73,8 +73,60 @@ class Solution {
             backtrace(res, temp, candidates, i, target - candidates[i]);
             temp.remove(temp.size() - 1);
         }
+    }
+}
+```
 
+Go
+
+```go
+func combinationSum(candidates []int, target int) [][]int {
+    res := [][]int{}
+    var dfs func(index, remain int, temp []int)
+    dfs = func(index, remain int, temp []int){
+        if remain == 0 {
+            res = append(res, slices.Clone(temp))	// 一定要复制一份
+            return
+        }
+        if remain < 0 {
+            return
+        }
+        for i := index; i < len(candidates); i++ {
+            temp = append(temp, candidates[i])
+            dfs(i, remain - candidates[i], temp)
+            temp = temp[:len(temp) - 1]
+        }
     }
+    dfs(0, target, []int{})
+    return res
+}
+```
+
 
+
+
+
+**方法二：选或不选**
+
+```go
+func combinationSum(candidates []int, target int) [][]int {
+    res := [][]int{}
+    var dfs func(index, remain int, temp []int)
+    dfs = func(index, remain int, temp []int){
+        if index >= len(candidates) || remain < 0 {
+            return
+        }
+        if remain == 0 {
+            res = append(res, slices.Clone(temp))
+            return
+        }
+        dfs(index + 1, remain, temp)
+        temp = append(temp, candidates[index])
+        dfs(index, remain - candidates[index], temp)
+        temp = temp[:len(temp) - 1]
+    }
+    dfs(0, target, []int{})
+    return res
 }
-```
+```
+