upate

Author: dingjikerbo

README.md

@@ -404,5 +404,6 @@
 |849|[Maximize Distance to Closest Person](https://leetcode.com/problems/maximize-distance-to-closest-person/)|[Java](leetcode/solution/src/MaximizeDistanceToClosestPerson.java)|80||
 |857|[Minimum Cost to Hire K Workers](https://leetcode.com/problems/minimum-cost-to-hire-k-workers/)|[Java](leetcode/solution/src/MinimumCostToHireKWorkers.java)|70||
 |872|[Leaf-Similar Trees](https://leetcode.com/problems/leaf-similar-trees/)|[Java](leetcode/solution/src/LeafSimilarTrees.java)|80||
+|889|[Construct Binary Tree from Preorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-postorder-traversal/)|[Java](leetcode/solution/src/ConstructBinaryTreeFromPreorderAndPostorderTraversal.java)|80||
 |904|[Fruit Into Baskets](https://leetcode.com/problems/fruit-into-baskets/)|[Java](leetcode/solution/src/FruitIntoBaskets.java)|90||
 |929|[Unique Email Addresses](https://leetcode.com/problems/unique-email-addresses/)|[Java](leetcode/solution/src/UniqueEmailAddresses.java)|90||

leetcode/solution/src/BinaryTreePostorderTraversal.java

@@ -23,52 +23,12 @@ public List<Integer> postorderTraversal(TreeNode root) {
         return results;
     }
 
-
-    public ArrayList<Integer> postorderTraversal2(TreeNode root) {
-        ArrayList<Integer> result = new ArrayList<Integer>();
-        Stack<TreeNode> stack = new Stack<TreeNode>();
-        TreeNode prev = null; // previously traversed node
-        TreeNode curr = root;
-
-        if (root == null) {
-            return result;
-        }
-
-        stack.push(root);
-        while (!stack.empty()) {
-            curr = stack.peek();
-            if (prev == null || prev.left == curr || prev.right == curr) { // traverse down the tree
-                if (curr.left != null) {
-                    stack.push(curr.left);
-                } else if (curr.right != null) {
-                    stack.push(curr.right);
-                }
-            } else if (curr.left == prev) { // traverse up the tree from the left
-                if (curr.right != null) {
-                    stack.push(curr.right);
-                }
-            } else { // traverse up the tree from the right
-                result.add(curr.val);
-                stack.pop();
-            }
-            prev = curr;
-        }
-
-        return result;
-    }
-
-    public List<Integer> postorderTraversal3(TreeNode root) {
+    // root为null表示栈顶的左子树都访问完了，该看右子树了
+    public List<Integer> postorderTraversal2(TreeNode root) {
         List<Integer> result = new ArrayList<>();
-
-        if (root == null) {
-            return result;
-        }
-
         Stack<TreeNode> stack = new Stack<>();
 
-        TreeNode last = null;
-
-        while (!stack.isEmpty() || root != null) {
+        for (TreeNode last = null; !stack.isEmpty() || root != null; ) {
             if (root != null) {
                 stack.push(root);
                 root = root.left;

leetcode/solution/src/ConstructBinaryTreeFromPreorderAndPostorderTraversal.java

@@ -0,0 +1,29 @@
+import java.util.HashMap;
+
+public class ConstructBinaryTreeFromPreorderAndPostorderTraversal {
+
+    /**
+     * 这里先记录一下post每个数对应的索引，免得每次去找
+     * 不过找找也没关系，因为每个元素不会重复找
+     */
+    public TreeNode constructFromPrePost(int[] pre, int[] post) {
+        HashMap<Integer, Integer> map = new HashMap<>();
+        for (int i = 0; i < post.length; i++) {
+            map.put(post[i], i);
+        }
+        return helper(pre, 0, pre.length - 1, post, 0, post.length - 1, map);
+    }
+
+    private TreeNode helper(int[] pre, int prestart, int preend, int[] post, int poststart, int postend, HashMap<Integer, Integer> map) {
+        if (prestart > preend || poststart > postend) {
+            return null;
+        }
+        TreeNode root = new TreeNode(pre[prestart]);
+        if (prestart + 1 <= preend) {
+            int len = map.get(pre[prestart + 1]) - poststart + 1;
+            root.left = helper(pre, prestart + 1, prestart + len, post, poststart, poststart + len - 1, map);
+            root.right = helper(pre, prestart + len + 1, preend, post, poststart + len, postend - 1, map);
+        }
+        return root;
+    }
+}

leetcode/solution/src/FindMinimumInRotatedSortedArray.java

@@ -1,5 +1,14 @@
 public class FindMinimumInRotatedSortedArray {
 
+    /**
+     * 由于[left, right]区间内包含了最小值，nums[left]通常是比nums[right]大的
+     * 如果nums[left]<nums[right]只有一个可能，就是nums[left]最小
+     *
+     * TestCase
+     * [1, 2]
+     * [2, 1]
+     * [1]
+     */
     public int findMin(int[] nums) {
         int left = 0, right = nums.length - 1;
         while (left < right) {

leetcode/solution/src/SearchForARange.java

@@ -21,6 +21,7 @@ public int[] searchRange(int[] nums, int target) {
         };
     }
 
+    // 测区间只有1个数或两个数的情况
     private int firstHigherEqual(int[] nums, int target) {
         int left = 0, right = nums.length;
         while (left < right) {
@@ -33,52 +34,4 @@ private int firstHigherEqual(int[] nums, int target) {
         }
         return left;
     }
-
-    public int[] searchRange2(int[] nums, int target) {
-        if (nums.length == 0) {
-            return new int[]{-1, -1};
-        }
-        return new int[] {
-                lowerBound(nums, target),
-                upperBound(nums, target)
-        };
-    }
-
-    /**
-     * lowerBound和upperBound的TestCase
-     * [1,3],3
-     * [1,3],1
-     * [2,2],2
-     */
-    public static int lowerBound(int[] nums, int target) {
-        int left = 0, right = nums.length - 1;
-
-        while (left < right) {
-            int mid = left + ((right - left) >> 1);
-
-            if (target > nums[mid]) {
-                left = mid + 1;
-            } else {
-                right = mid;
-            }
-        }
-
-        return nums[left] == target ? left : -1;
-    }
-
-    public static int upperBound(int[] nums, int target) {
-        int left = 0, right = nums.length - 1;
-
-        while (left < right) {
-            int mid = left + ((right - left) >> 1) + 1;
-
-            if (target < nums[mid]) {
-                right = mid - 1;
-            } else {
-                left = mid;
-            }
-        }
-
-        return nums[right] == target ? right : -1;
-    }
 }

leetcode/solution/src/SimplifyPath.java

@@ -5,9 +5,6 @@ public class SimplifyPath {
 
     public String simplifyPath(String path) {
         String[] ss = path.split("/");
-        /**
-         * 注意这里要用双端队列，因为后面要生成路径需要从前往后
-         */
         Deque<String> queue = new LinkedList<>();
         for (String s : ss) {
             /**

leetcode/src/Main.java

@@ -6,36 +6,14 @@
 public class Main {
 
     public static class Solution {
-        public int lengthOfLongestSubstring(String s) {
-            HashMap<Character, Integer> map = new HashMap<>();
-            int max = 0;
-            for (int i = 0, j = 0; i < s.length(); i++) {
-                char c = s.charAt(i);
-                map.put(c, map.getOrDefault(c, 0) + 1);
-                for ( ; j < i && map.get(c) > 1; j++) {
-                    char cc = s.charAt(j);
-                    map.put(cc, map.get(cc) - 1);
-                }
-                max = Math.max(max, i - j + 1);
-            }
-            return max;
-        }
 
-        public int lengthOfLongestSubstring(String s) {
-            int[] count = new int[256];
-            int max = 0;
-            for (int i = 0, j = 0; i < s.length(); i++) {
-                char c = s.charAt(i);
-                count[c]++;
-                for ( ; j < i && count[c] > 1; j++) {
-                    count[s.charAt(j)]--;
-                }
-                max = Math.max(max, i - j + 1);
+        public int myAtoi(String str) {
+            str = str.trim();
+            if (str.length() == 0) {
+                return
             }
-            return max;
         }
 
-    }
 
 
     public static void main(String[] args) {