20190315

Author: mJackie

code/lc113.java

@@ -0,0 +1,39 @@
+package code;
+
+import java.util.ArrayList;
+import java.util.List;
+/*
+ * 113. Path Sum II
+ * 题意：找从root到叶子节点和为sum的路径
+ * 难度：Medium
+ * 分类：Tree, Depth-first Search
+ * 思路：回溯，注意因为节点上可能正值，可能负值，所以不能剪枝
+ * Tips：
+ */
+public class lc113 {
+    public class TreeNode {
+        int val;
+        TreeNode left;
+        TreeNode right;
+        TreeNode(int x) {
+            val = x;
+        }
+    }
+    public List<List<Integer>> pathSum(TreeNode root, int sum) {
+        List<List<Integer>> res = new ArrayList<>();
+        helper(res, root, sum, 0, new ArrayList<>());
+        return res;
+    }
+    public void helper(List<List<Integer>> res, TreeNode root, int sum, int curr, List<Integer> curr_ls) {
+        if(root==null) return;
+        curr_ls.add(root.val);
+        if(curr+root.val==sum && root.left==null && root.right==null) { //到叶子节点
+            res.add(new ArrayList<>(curr_ls));
+            curr_ls.remove(curr_ls.size()-1);
+            return;
+        }
+        helper(res, root.left, sum, curr+root.val, curr_ls);
+        helper(res, root.right, sum, curr+root.val, curr_ls);
+        curr_ls.remove(curr_ls.size()-1);
+    }
+}

code/lc31.java

@@ -28,7 +28,7 @@ public static void nextPermutation(int[] nums) {
             //从这个数之后的数中找出第一个比x大的数
             int n = nums[ptr];
             int ptr2 = ptr;
-            for(int i=ptr+1; i<nums.length; i++){
+            for(int i=ptr+1; i<nums.length; i++){   //这不用这么麻烦，后边的数有序的，这可以简化
                 if( nums[i]>nums[ptr-1] && nums[i]<=n ) {//注意 <= {2,3,1,3,3}
                     n = nums[i];
                     ptr2 = i;

code/lc49.java

@@ -14,7 +14,7 @@ public List<List<String>> groupAnagrams(String[] strs) {
         HashMap<String,List<String>> m = new HashMap();
         for (int i = 0; i < strs.length ; i++) {
             char[] chs = strs[i].toCharArray();
-            Arrays.sort(chs);
+            Arrays.sort(chs);   //对字符串排序
             String key = String.valueOf(chs);
             if(m.containsKey(key))
                 m.get(key).add(strs[i]);

readme.md

@@ -89,15 +89,18 @@ LeetCode 指南
 | 095 [Java](./code/lc95.java)
 | 096 [Java](./code/lc96.java)
 | 098 [Java](./code/lc98.java)
+| 100 [Java](./code/lc100.java)
 | 101 [Java](./code/lc101.java)
 | 102 [Java](./code/lc102.java)
 | 103 [Java](./code/lc103.java)
 | 104 [Java](./code/lc104.java)
 | 105 [Java](./code/lc105.java)
 | 108 [Java](./code/lc108.java)
+| 113 [Java](./code/lc113.java)
 | 114 [Java](./code/lc114.java)
 | 116 [Java](./code/lc116.java)
 | 118 [Java](./code/lc118.java)
+| 119 [Java](./code/lc119.java)
 | 120 [Java](./code/lc120.java)
 | 121 [Java](./code/lc121.java)
 | 122 [Java](./code/lc122.java)