refactor: 0216.组合总和III.md

Author: qiufeihong2018

problems/0216.组合总和III.md

@@ -417,39 +417,82 @@ func dfs(k, n int, start int, sum int) {
 ```
 
 ### JavaScript
+- 未剪枝：
 
 ```js
 /**
  * @param {number} k
  * @param {number} n
  * @return {number[][]}
  */
-var combinationSum3 = function(k, n) {
-    let res = [];
-    let path = [];
-    let sum = 0;
-    const dfs = (path,index) => {
-        // 剪枝操作
-        if (sum > n){
-            return
-        }
-        if (path.length == k) {
-            if(sum == n){
-                res.push([...path]);
-                return
-            }
-        }
-        for (let i = index; i <= 9 - (k-path.length) + 1;i++) {
-            path.push(i);
-            sum = sum + i;
-            index += 1;
-            dfs(path,index);
-            sum -= i
-            path.pop()
-        }
+var combinationSum3 = function (k, n) {
+  // 回溯法
+  let result = [],
+    path = [];
+  const backtracking = (_k, targetSum, sum, startIndex) => {
+    // 终止条件
+    if (path.length === _k) {
+      if (sum === targetSum) {
+        result.push(path.slice());
+      }
+      // 如果总和不相等，就直接返回
+      return;
     }
-    dfs(path,1);
-    return res
+
+    // 循环当前节点，因为只使用数字1到9，所以最大是9
+    for (let i = startIndex; i <= 9; i++) {
+      path.push(i);
+      sum += i;
+      // 回调函数
+      backtracking(_k, targetSum, sum, i + 1);
+      // 回溯
+      sum -= i;
+      path.pop();
+    }
+  };
+  backtracking(k, n, 0, 1);
+  return result;
+};
+```
+
+- 剪枝：
+
+```js
+/**
+ * @param {number} k
+ * @param {number} n
+ * @return {number[][]}
+ */
+var combinationSum3 = function (k, n) {
+  // 回溯法
+  let result = [],
+    path = [];
+  const backtracking = (_k, targetSum, sum, startIndex) => {
+    if (sum > targetSum) {
+      return;
+    }
+    // 终止条件
+    if (path.length === _k) {
+      if (sum === targetSum) {
+        result.push(path.slice());
+      }
+      // 如果总和不相等，就直接返回
+      return;
+    }
+
+    // 循环当前节点，因为只使用数字1到9，所以最大是9
+    for (let i = startIndex; i <= 9 - (_k - path.length) + 1; i++) {
+      path.push(i);
+      sum += i;
+      // 回调函数
+      backtracking(_k, targetSum, sum, i + 1);
+      // 回溯
+      sum -= i;
+      path.pop();
+    }
+  };
+  backtracking(k, n, 0, 1);
+  return result;
 };
 ```