添加39. 组合总和JavaScript版本

problems/0039.组合总和.md

@@ -286,30 +286,30 @@ class Solution:
 ```
 Go：
 
-JavaScript
+JavaScript：
+
 ```js
-var strStr = function (haystack, needle) {
-  if (needle === '') {
-    return 0;
-  }
-
-  let hayslen = haystack.length;
-  let needlen = needle.length;
-
-  if (haystack === '' || hayslen < needlen) {
-    return -1;
-  }
-
-  for (let i = 0; i <= hayslen - needlen; i++) {
-    if (haystack[i] === needle[0]) {
-      if (haystack.substr(i, needlen) === needle) {
-        return i;
-      }
+var combinationSum = function(candidates, target) {
+    const res = [], path = [];
+    candidates.sort(); // 排序
+    backtracking(0, 0);
+    return res;
+    function backtracking(j, sum) {
+        if (sum > target) return;
+        if (sum === target) {
+            res.push(Array.from(path));
+            return;
+        }
+        for(let i = j; i < candidates.length; i++ ) {
+            const n = candidates[i];
+            if(n > target - sum) continue;
+            path.push(n);
+            sum += n;
+            backtracking(i, sum);
+            path.pop();
+            sum -= n;
+        }
     }
-    if (i === hayslen - needlen) {
-      return -1;
-    }
-  }
 };
 ```