增加code

Author: starsingchow

java/28.找出字符串中第一个匹配项的下标.java

@@ -0,0 +1,37 @@
+/*
+ * @lc app=leetcode.cn id=28 lang=java
+ *
+ * [28] 找出字符串中第一个匹配项的下标
+ */
+
+// @lc code=start
+class Solution {
+    public int strStr(String haystack, String needle) {
+        if(haystack == null || needle == null || haystack.length() == 0 || needle.length() == 0) {
+            return -1;
+        }
+
+        int hLen = haystack.length();
+        int nLen = needle.length();
+        int i = 0;
+        int j = 0;
+        int temp = i;
+        while(i < hLen && j < nLen) {
+            if(haystack.charAt(i) == needle.charAt(j)) {
+                i++;
+                j++;
+                if(j == nLen) {
+                    return temp;
+                }
+            } else {
+                i = temp+1;
+                j = 0;
+                temp = i;
+            }
+        }
+
+        return -1;
+    }
+}
+// @lc code=end
+

java/78.子集.java

@@ -0,0 +1,33 @@
+/*
+ * @lc app=leetcode.cn id=78 lang=java
+ *
+ * [78] 子集
+ */
+
+// @lc code=start
+class Solution {
+    public List<List<Integer>> subsets(int[] nums) {
+        List<List<Integer>> result = new ArrayList<>();
+
+        if(nums == null) {
+            return null;
+        }
+
+        List<Integer> list = new ArrayList();
+
+        backtrack(nums, 0, nums.length, list, result);
+        return result;
+    }
+
+    private void backtrack(int[] nums, int index, int nLen,List<Integer> list, List<List<Integer>> result) {
+        result.add(new ArrayList(list));
+
+        for(int i = index; i < nLen; i++) {
+            list.add(nums[i]);
+            backtrack(nums, i+1, nLen, list, result);
+            list.remove(list.size()-1);
+        }
+    }
+}
+// @lc code=end
+