提交

Author: YorkPeng

160.相交链表.java

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+/*
+ * @lc app=leetcode.cn id=160 lang=java
+ *
+ * [160] 相交链表
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) {
+ *         val = x;
+ *         next = null;
+ *     }
+ * }
+ */
+public class Solution {
+    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
+        ListNode temp = null;
+        ListNode head1 = headA;
+        ListNode head2 = headB;
+        int countA = 0;
+        int countB= 0;
+        while(head1 != null){
+            countA++;
+            head1 = head1.next;
+        }
+        while(head2 != null){
+            countB++;
+            head2 = head2.next;
+        }
+
+        head1 = headA;
+        head2= headB;
+        if(countA > countB){
+            while(countA>countB){
+              head1 = head1.next;
+              countA--;
+            }
+        }else if(countB > countA){
+            while(countB > countA){
+                head2 = head2.next;
+                countB--;
+            }
+        }
+
+        while(head1!=null && head2!=null){
+            if(head1 == head2){
+                temp = head1;
+                break;
+            }
+            head1 =head1.next;
+            head2 = head2.next;
+        }
+
+        return temp;
+    }
+}
+// @lc code=end
+

235.二叉搜索树的最近公共祖先.java

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+/*
+ * @lc app=leetcode.cn id=235 lang=java
+ *
+ * [235] 二叉搜索树的最近公共祖先
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    TreeNode temp;
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        las(root, p, q);
+        return temp;
+    }
+    private void las(TreeNode root, TreeNode p, TreeNode q){
+        if((root.val - p.val) * (root.val - q.val) <=0){
+            temp = root;
+        }
+        if(root.val > p.val && root.val > q.val){
+            las(root.left,p,q);
+        }
+        if(root.val < p.val && root.val < q.val){
+            las(root.right, p, q);
+        }
+    }
+}
+// @lc code=end
+

532.数组中的k-diff数对.java

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+import java.util.HashSet;
+/*
+ * @lc app=leetcode.cn id=532 lang=java
+ *
+ * [532] 数组中的K-diff数对
+ */
+import java.util.Map;
+
+// @lc code=start
+class Solution {
+
+    public int findPairs(int[] nums, int k) {
+        Map<Integer,Integer> map = new HashMap<>();
+        int count = 0;
+        if(k < 0){
+            return 0;
+        }
+        for(int i = 0; i < nums.length;i++){
+            map.putIfAbsent(nums[i], 0);
+            map.put(nums[i], map.get(nums[i]) + 1);
+        }
+        for(int i:map.keySet()){
+            if(k == 0){
+                if(map.get(i) > 1){
+                    count++;
+                }
+            }else{
+                if(map.containsKey(i + k)){
+                    count++;
+                }
+            }
+        }
+        return count;
+    }
+}
+// @lc code=end
+

729.我的日程安排表-i.java

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+import java.util.ArrayList;
+
+/*
+ * @lc app=leetcode.cn id=729 lang=java
+ *
+ * [729] 我的日程安排表 I
+ */
+
+// @lc code=start
+class MyCalendar {
+
+    List<int[]> list;
+
+    public MyCalendar() {
+        list = new ArrayList<>();
+    }
+    
+    public boolean book(int start, int end) {
+        for(int[] array:list){
+            if(start < array[1] && end > array[0] ){
+                return false;
+            }
+        }
+        list.add(new int[]{start,end});
+        return true;
+    }
+}
+
+/**
+ * Your MyCalendar object will be instantiated and called as such:
+ * MyCalendar obj = new MyCalendar();
+ * boolean param_1 = obj.book(start,end);
+ */
+// @lc code=end
+

笔记.md

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+# 笔记
+
+## #235 二叉搜索树的最近公共祖先
+
+```java
+class Solution {
+    TreeNode temp;
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        las(root, p, q);
+        return temp;
+    }
+    private void las(TreeNode root, TreeNode p, TreeNode q){
+        if((root.val - p.val) * (root.val - q.val) <=0){
+            temp = root;
+        }
+        if(root.val > p.val && root.val > q.val){
+            las(root.left,p,q);
+        }
+        if(root.val < p.val && root.val < q.val){
+            las(root.right, p, q);
+        }
+    }
+}
+```
+
+​	此算法利用到了二叉搜索树的性质。如果搜寻的两个节点都要大于根节点，那么其公共祖先必定在根节点的右手边。同理当两个节点都要小于根节点的话，其公共祖先必定在左手边。
+
+​	当要搜寻的两个节点位于根节点的左右两边的话（(root.val - p.val) * (root.val - q.val) <= 0），该跟节点为他们的公共祖先。
+
+​	若不使用该方法的话，可以先使用两个linkedlist分别存储寻找p和q节点过程中经过的节点，然后再进行对比，找到最后一个相同位置的节点。
+
+## #532 数组中的K-diff数对
+
+```java
+class Solution {
+
+    public int findPairs(int[] nums, int k) {
+        Map<Integer,Integer> map = new HashMap<>();
+        int count = 0;
+        if(k < 0){
+            return 0;
+        }
+        for(int i = 0; i < nums.length;i++){
+            map.putIfAbsent(nums[i], 0);
+            map.put(nums[i], map.get(nums[i]) + 1);
+        }
+        for(int i:map.keySet()){
+            if(k == 0){
+                if(map.get(i) > 1){
+                    count++;
+                }
+            }else{
+                if(map.containsKey(i + k)){
+                    count++;
+                }
+            }
+        }
+        return count;
+    }
+}
+```
+
+跟两数之和类似，使用map进行数量的统计。