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QuinnDK · May 13, 2021 · d2dc300 · d2dc300
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diff --git a/problems/0056.合并区间.md b/problems/0056.合并区间.md
@@ -137,7 +137,35 @@ public:
 
 
 Java：
+```java
+class Solution {
+    public int[][] merge(int[][] intervals) {
+        List<int[]> res = new LinkedList<>();
+        Arrays.sort(intervals, new Comparator<int[]>() {
+            @Override
+            public int compare(int[] o1, int[] o2) {
+                if (o1[0] != o2[0]) {
+                    return Integer.compare(o1[0],o2[0]);
+                } else {
+                    return Integer.compare(o1[1],o2[1]);
+                }
+            }
+        });
 
+        int start = intervals[0][0];
+        for (int i = 1; i < intervals.length; i++) {
+            if (intervals[i][0] > intervals[i - 1][1]) {
+                res.add(new int[]{start, intervals[i - 1][1]});
+                start = intervals[i][0];
+            } else {
+                intervals[i][1] = Math.max(intervals[i][1], intervals[i - 1][1]);
+            }
+        }
+        res.add(new int[]{start, intervals[intervals.length - 1][1]});
+        return res.toArray(new int[res.size()][]);
+    }
+}
+```
 
 Python：
 
@@ -151,4 +179,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
diff --git a/problems/0070.爬楼梯完全背包版本.md b/problems/0070.爬楼梯完全背包版本.md
@@ -127,7 +127,23 @@ public:
 
 
 Java：
+```java
+class Solution {
+    public int climbStairs(int n) {
+        int[] dp = new int[n + 1];
+        int[] weight = {1,2};
+        dp[0] = 1;
+
+        for (int i = 0; i <= n; i++) {
+            for (int j = 0; j < weight.length; j++) {
+                if (i >= weight[j]) dp[i] += dp[i - weight[j]];
+            }
+        }
 
+        return dp[n];
+    }
+}
+```
 
 Python：
 
@@ -141,4 +157,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
diff --git a/problems/0098.验证二叉搜索树.md b/problems/0098.验证二叉搜索树.md
@@ -254,6 +254,19 @@ public:
 
 
 Java：
+```java
+class Solution {
+    public boolean isValidBST(TreeNode root) {
+        return isValidBST_2(root, Long.MIN_VALUE, Long.MAX_VALUE);
+    }
+
+    public boolean isValidBST_2 (TreeNode root, long lo, long hi) {
+        if (root == null) return true;
+        if (root.val >= hi || root.val <= lo) return false;
+        return isValidBST_2(root.left,lo,root.val) && isValidBST_2(root.right,root.val,hi);
+    }
+}
+```
 
 
 Python：
@@ -268,4 +281,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
diff --git a/problems/0104.二叉树的最大深度.md b/problems/0104.二叉树的最大深度.md
@@ -231,6 +231,18 @@ public:
 
 
 Java：
+```java
+class Solution {
+    public int maxDepth(TreeNode root) {
+        if (root == null) {
+            return 0;
+        }
+        int leftdeep = maxDepth(root.left);
+        int rightdeep = maxDepth(root.right);
+        return 1+Math.max(leftdeep,rightdeep);
+    }
+}
+```
 
 
 Python：
@@ -245,4 +257,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
diff --git a/problems/0106.从中序与后序遍历序列构造二叉树.md b/problems/0106.从中序与后序遍历序列构造二叉树.md
@@ -582,6 +582,47 @@ tree2 的前序遍历是[1 2 3]， 后序遍历是[3 2 1]。
 
 
 Java：
+```java
+class Solution {
+    public TreeNode buildTree(int[] inorder, int[] postorder) {
+        if (inorder.length == 0 || postorder.length == 0) return null;
+        return buildTree(inorder, postorder,0,inorder.length,0,postorder.length);
+    }
+
+    private TreeNode buildTree(int[] inorder, int[] postorder, int infrom, int into,
+                                      int postfrom, int postto) {
+        if (postfrom == postto) return null;
+
+        int rootValue = postorder[postto - 1];
+        TreeNode root = new TreeNode(rootValue);
+
+        if (postfrom + 1 == postto) return root;
+
+        int splitNum = postto - 1;
+        for (int i = infrom; i < into; i++) {
+            if (inorder[i] == rootValue) {
+                splitNum = i;
+                break;
+            }
+        }
+
+        int inLeftBegin = infrom;
+        int inLeftEnd = splitNum;
+        int inRightBegin = splitNum + 1;
+        int inRightEnd = into;
+
+        int postLeftBegin = postfrom;
+        int postLeftEnd = postLeftBegin + (splitNum - inLeftBegin);
+        int postRightBegin = postLeftBegin + (splitNum - inLeftBegin);
+        int postRightEnd = postto - 1;
+
+        root.left = buildTree(inorder,postorder,inLeftBegin,inLeftEnd,postLeftBegin,postLeftEnd);
+        root.right = buildTree(inorder,postorder,inRightBegin,inRightEnd,postRightBegin,postRightEnd);
+
+        return root;
+    }
+}
+```
 
 
 Python：
@@ -596,4 +637,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
diff --git a/problems/0108.将有序数组转换为二叉搜索树.md b/problems/0108.将有序数组转换为二叉搜索树.md
@@ -209,6 +209,26 @@ public:
 
 
 Java：
+```java
+class Solution {
+    public TreeNode sortedArrayToBST(int[] nums) {
+        return sortArr(nums,0,nums.length);
+    }
+
+    private TreeNode sortArr(int[] nums, int lo, int hi) {
+        if (lo == hi) return null;
+        int rootIdx = (lo + hi)/2;
+
+        int rootValue = nums[rootIdx];
+        TreeNode root = new TreeNode(rootValue);
+
+        root.left = sortArr(nums,lo,rootIdx);
+        root.right = sortArr(nums,rootIdx+1,hi);
+
+        return root;
+    }
+}
+```
 
 
 Python：
@@ -223,4 +243,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
diff --git a/problems/0110.平衡二叉树.md b/problems/0110.平衡二叉树.md
@@ -355,6 +355,29 @@ public:
 
 
 Java：
+```java
+class Solution {
+    boolean flag = true;
+    public boolean isBalanced(TreeNode root) {
+        high(root);
+        return flag;
+    }
+
+    private int high (TreeNode root) {
+        if (root == null) return 0;
+        if (flag) {
+            int left = high(root.left);
+            int right = high(root.right);
+
+            if (Math.abs(left - right) > 1) flag = false;
+
+            return Math.max(left,right) + 1;
+        } else {
+            return -1;
+        }
+    }
+}
+```
 
 
 Python：
@@ -369,4 +392,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
diff --git a/problems/0111.二叉树的最小深度.md b/problems/0111.二叉树的最小深度.md
@@ -194,6 +194,20 @@ public:
 
 
 Java：
+```java
+class Solution {
+    public int minDepth(TreeNode root) {
+        if (root == null) return 0;
+        int leftDeep = minDepth(root.left);
+        int rightDeep = minDepth(root.right);
+
+        if (root.left == null && root.right != null) return 1+rightDeep;
+        if (root.left != null && root.right == null) return 1+leftDeep;
+
+        return Math.min(leftDeep,rightDeep)+1;
+    }
+}
+```
 
 Python：
 

diff --git a/problems/0112.路径总和.md b/problems/0112.路径总和.md
@@ -305,6 +305,24 @@ public:
 
 
 Java：
+```java
+class Solution {
+    private boolean flag = false;
+    public boolean hasPathSum(TreeNode root, int targetSum) {
+        has_2(root,targetSum);
+        return flag;
+    }
+
+    public void has_2 (TreeNode root, int count) {
+        if (root == null) return;
+        if (root.left == null && root.right == null && count == root.val) {
+            flag = true;
+        }
+        if (root.left != null) has_2(root.left,count - root.val);
+        if (root.right != null) has_2(root.right,count - root.val);
+    }
+}
+```
 
 
 Python：
@@ -387,4 +405,4 @@ let pathSum = function (root, targetSum) {
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
diff --git a/problems/0122.买卖股票的最佳时机II.md b/problems/0122.买卖股票的最佳时机II.md
@@ -135,7 +135,23 @@ public:
 
 
 Java：
-
+```java
+class Solution {
+    public int maxProfit(int[] prices) {
+        int sum = 0;
+        int profit = 0;
+        int buy = prices[0];
+        for (int i = 1; i < prices.length; i++) {
+            profit = prices[i] - buy;
+            if (profit > 0) {
+                sum += profit;
+            }
+            buy = prices[i];
+        }
+        return sum;
+    }
+}
+```
 
 Python：
 
@@ -149,4 +165,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
diff --git a/problems/0134.加油站.md b/problems/0134.加油站.md
@@ -199,7 +199,28 @@ public:
 
 
 Java：
+```java
+class Solution {
+    public int canCompleteCircuit(int[] gas, int[] cost) {
+        int sum = 0;
+        int min = 0;
+        for (int i = 0; i < gas.length; i++) {
+            sum += (gas[i] - cost[i]);
+            min = Math.min(sum, min);
+        }
+
+        if (sum < 0) return -1;
+        if (min >= 0) return 0;
+
+        for (int i = gas.length - 1; i > 0; i--) {
+            min += (gas[i] - cost[i]);
+            if (min >= 0) return i;
+        }
 
+        return -1;
+    }
+}
+```
 
 Python：
 
@@ -213,4 +234,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>