LeetCode&&剑指offer
2021-08-03 21:15:22 星期二
509. 斐波那契数
https://leetcode-cn.com/problems/fibonacci-number/submissions/
class Solution {
public int fib(int n) {
if(n < 2){
return n;
}
int f = 0, s = 1;
for(int i = 2; i <= n; i++){
int t = f + s;
f = s;
s = t;
}
return s;
}
}
JZ50 数组中重复的数字
https://www.nowcoder.com/practice/6fe361ede7e54db1b84adc81d09d8524?tpId=13&tqId=11203&tab=answerKey&from=cyc_github
大佬总结:
https://github.com/CyC2018/CS-Notes/blob/master/notes/3. 数组中重复的数字.md
import java.util.*;
public class Solution {
/**
* 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
*
*
* @param numbers int整型一维数组
* @return int整型
*/
//方法一
public int duplicate (int[] numbers) {
int[] tmp = new int[numbers.length];
for(int i = 0; i < numbers.length; i++){
if(tmp[numbers[i]] > 0){
return numbers[i];
}
tmp[numbers[i]]++;
}
return -1;
}
//方法二
public int duplicate (int[] numbers) {
for(int i = 0; i < numbers.length; i++){
while(i != numbers[i]){
if(numbers[i] == numbers[numbers[i]]){
return numbers[i];
}
int t = numbers[i];
numbers[i] = numbers[numbers[i]];
numbers[t] = t;
}
}
return -1;
}
}
2021-08-04 21:32:21 星期三
167. 两数之和 II - 输入有序数组
class Solution {
public int[] twoSum(int[] numbers, int target) {
int i = 0, j = numbers.length - 1;
while (i < j){
if (numbers[i] + numbers[j] == target) return new int[] {i + 1, j + 1};
if (numbers[i] + numbers[j] > target){
j--;
continue;
}else {
i++;
continue;
}
}
return null;
}
}
633. 平方数之和
class Solution {
public boolean judgeSquareSum(int c) {
int sqrt = (int) Math.sqrt(c);
int i = 0, j = sqrt;
while (i <= j) {
if (i*i + j*j == c) return true;
if (i*i + j*j > c){
j--;
}else {
i++;
}
}
return false;
}
}
345. 反转字符串中的元音字母
class Solution {
public String reverseVowels(String s) {
List<Character> t = Arrays.asList('a', 'o', 'e', 'i', 'u', 'A', 'O', 'E', 'I' ,'U');
char[] array = s.toCharArray();
int i = 0, j = array.length - 1;
while (i <= j){
if (t.contains(array[i]) && t.contains(array[j])){
char tmp = array[i];
array[i] = array[j];
array[j] = tmp;
i++;
j--;
}else if (t.contains(array[i])){
j--;
}else if (t.contains(array[j])){
i++;
}else {
i++;
j--;
}
}
return new String(array);
}
}
2021-08-05 23:14:32 星期四
680. 验证回文字符串 Ⅱ
class Solution {
public boolean validPalindrome(String s) {
if (s == null) return false;
if (s.length() < 2) return true;
char[] array = s.toCharArray();
int i = 0, j = array.length - 1;
while (i < j) {
if (array[i] == array[j]) {
i++;
j--;
continue;
} else {
return isPalindrome(new String(array, i, j - i)) || isPalindrome(new String(array, i + 1, j - i));
}
}
return true;
}
public boolean isPalindrome(String s) {
int i = 0, j = s.length() - 1;
while (i < j) {
if (s.charAt(i) != s.charAt(j)) return false;
i++;
j--;
}
return true;
}
}
88. 合并两个有序数组
class Solution {
public void merge(int[] nums1, int m, int[] nums2, int n) {
int i = m - 1, j = n - 1, k = m + n - 1;
while (i >= 0 && j >= 0){
if (nums1[i] >= nums2[j]){
nums1[k--] = nums1[i--];
}else {
nums1[k--] = nums2[j--];
}
}
if (i >= 0){
while (k >= 0){
nums1[k--] = nums1[i--];
}
}else {
while (k >= 0){
nums1[k--] = nums2[j--];
}
}
}
}
141. 环形链表
public class Solution {
public boolean hasCycle(ListNode head) {
if (head == null || head.next == null) return false;
ListNode h1 = head, h2 = head.next;
while (h1 != null && h2 != null && h2.next != null){
if (h1 == h2) return true;
h1 = h1.next;
h2 = h2.next.next;
}
return false;
}
}
2021-08-07 22:49:23 星期六
524. 通过删除字母匹配到字典里最长单词
class Solution {
public String findLongestWord(String s, List<String> dictionary) {
if(dictionary == null) return "";
Collections.sort(dictionary);
int i = 0, max = 0;
String result = "";
while (i < dictionary.size()){
if (isSubStr(s, dictionary.get(i)) && dictionary.get(i).length() > max){
max = dictionary.get(i).length();
result = dictionary.get(i);
}
i++;
}
return result;
}
private boolean isSubStr(String s, String target){
int i = 0, j = 0;
while (i < s.length() && j < target.length()){
if (s.charAt(i) == target.charAt(j)){
j++;
}
i++;
}
return j == target.length();
}
}
215. 数组中的第K个最大元素
class Solution {
public int findKthLargest(int[] nums, int k) {
Arrays.sort(nums);
return nums[nums.length - k];
}
}
2021-08-08 10:57:32 星期日
20. 有效的括号
class Solution {
public boolean isValid(String s) {
char[] array = s.toCharArray();
Stack<Character> stack = new Stack<>();
for (char c : array) {
if (c == '(' || c == '[' || c == '{'){
stack.push(c);
}else {
if (stack.isEmpty()) return false;
switch (stack.pop()){
case '(':
if (c != ')') {
return false;
}
break;
case '[':
if (c != ']'){
return false;
}
break;
case '{':
if (c != '}'){
return false;
}
break;
}
}
}
return stack.isEmpty();
}
}
2021-08-09 21:10:23 星期一
232. 用栈实现队列
class MyQueue {
Stack<Integer> inStack = new Stack<>();
Stack<Integer> outStack = new Stack<>();
/** Initialize your data structure here. */
public MyQueue() {
}
/** Push element x to the back of queue. */
public void push(int x) {
inStack.push(x);
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
if (!outStack.isEmpty()) {
return outStack.pop();
}
while (!inStack.isEmpty()) {
outStack.push(inStack.pop());
}
return outStack.pop();
}
/** Get the front element. */
public int peek() {
if (!outStack.isEmpty()) {
return outStack.peek();
}
while (!inStack.isEmpty()) {
outStack.push(inStack.pop());
}
return outStack.peek();
}
/** Returns whether the queue is empty. */
public boolean empty() {
return outStack.isEmpty() && inStack.isEmpty();
}
}
69. x 的平方根
class Solution {
public int mySqrt(int x) {
if (x < 2) return x;
int left = 1, right = x;
while (left <= right){
int med = (left + right)/ 2;
int sqrt = x / med;
if (sqrt == med){
return med;
}else if (sqrt > med){
left = med + 1;
}else {
right = med - 1;
}
}
return right;
}
}
2021-09-17 23:54:14 星期五
455. 分发饼干
https://leetcode-cn.com/problems/assign-cookies/
import java.util.Arrays;
class Solution {
public int findContentChildren(int[] g, int[] s) {
Arrays.sort(g);
Arrays.sort(s);
int x = 0, y = 0;
while (x < g.length && y < s.length){
if (g[x] <= s[y]){
x++;
y++;
}else{
y++;
}
}
return x;
}
}
70. 爬楼梯
https://leetcode-cn.com/problems/climbing-stairs/
class Solution {
public int climbStairs(int n) {
if (n <= 2) return n;
int s1 = 1, s2 = 2;
for (int i = 3; i <= n; i++){
s2 += s1;
s1 = s2 - s1;
}
return s2;
}
}
120. 三角形最小路径和
https://leetcode-cn.com/problems/triangle/
class Solution {
public int minimumTotal(List<List<Integer>> triangle) {
if (triangle.size() == 1) {
return triangle.get(0).get(0);
}
for (int i = 1; i < triangle.size(); i++) {
for (int j = 0; j <= i; j++) {
if (j == 0) {
triangle.get(i).set(j, triangle.get(i).get(j) + triangle.get(i - 1).get(0));
} else if (j == i) {
triangle.get(i).set(j, triangle.get(i).get(j) + triangle.get(i - 1).get(j - 1));
} else {
triangle.get(i).set(j, triangle.get(i).get(j) + Math.min(triangle.get(i - 1).get(j - 1), triangle.get(i - 1).get(j)));
}
}
}
int min = triangle.get(triangle.size() - 1).get(0);
for (int i = 1; i < triangle.get(triangle.size() - 1).size(); i++) {
min = Math.min(min, triangle.get(triangle.size() - 1).get(i));
}
return min;
}
}
64. 最小路径和
https://leetcode-cn.com/problems/minimum-path-sum/
class Solution {
public int minPathSum(int[][] grid) {
for (int i = 1; i < grid.length; i++){
grid[i][0] += grid[i - 1][0];
}
for (int i = 1; i < grid[0].length; i++){
grid[0][i] += grid[0][i - 1];
}
for (int i = 1; i < grid.length; i++){
for (int j = 1; j < grid[i].length; j++){
grid[i][j] += Math.min(grid[i - 1][j], grid[i][j - 1]);
}
}
return grid[grid.length - 1][grid[grid.length - 1].length - 1];
}
}
2021-09-28 13:03:10 星期二
53. 最大子序和
https://leetcode-cn.com/problems/maximum-subarray/
class Solution {
public int maxSubArray(int[] nums) {
int max = nums[0];
for (int i = 1; i < nums.length; i++) {
nums[i] = Math.max(nums[i], nums[i - 1] + nums[i]);
max = Math.max(max, nums[i]);
}
return max;
}
}
2021-10-05 16:22:46 星期二
剑指 Offer II 024. 反转链表
https://leetcode-cn.com/problems/UHnkqh/
class Solution {
public ListNode reverseList(ListNode head) {
ListNode next = null, prev = null;
while (head != null){
next = head.next;
head.next = prev;
prev = head;
head = next;
}
return prev;
}
}
2021-10-06 16:08:45 星期三
414. 第三大的数
https://leetcode-cn.com/problems/third-maximum-number/
class Solution {
public int thirdMax(int[] nums) {
nums = Arrays.stream(nums).distinct().toArray();
Arrays.sort(nums);
if (nums.length < 3)
return nums[nums.length - 1];
return nums[nums.length - 3];
}
}
2021-10-08 16:11:34 星期五
剑指 Offer 27. 二叉树的镜像
https://leetcode-cn.com/problems/er-cha-shu-de-jing-xiang-lcof/
class Solution {
public TreeNode mirrorTree(TreeNode root) {
if (root == null) return root;
TreeNode t;
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
while (!queue.isEmpty()){
TreeNode poll = queue.poll();
t = poll.left;
poll.left = poll.right;
poll.right = t;
if (poll.left != null)
queue.offer(poll.left);
if (poll.right != null)
queue.offer(poll.right);
}
return root;
}
}
面试题 16.25. LRU 缓存
https://leetcode-cn.com/problems/lru-cache-lcci/
class LRUCache {
private List<Entry> entries;
private static int score = 0;
private int capacity;
class Entry{
int k;
int v;
int score;
public Entry(int k, int v) {
this.k = k;
this.v = v;
}
}
public LRUCache(int capacity) {
entries = new ArrayList<>(capacity);
this.capacity = capacity;
}
public int get(int key) {
for (Entry entry : entries) {
if (entry.k == key) {
entry.score = LRUCache.score++;
return entry.v;
}
}
return -1;
}
public void put(int key, int value) {
Entry entry = new Entry(key, value);
entry.score = LRUCache.score++;
int pos = contains(key);
if (pos != -1){
entries.set(pos, entry);
return;
}
if (entries.size() == capacity){
clear();
}
entries.add(entry);
}
private void clear(){
entries.sort(new Comparator<Entry>() {
@Override
public int compare(Entry o1, Entry o2) {
return o2.score - o1.score;
}
});
entries.remove(entries.size() - 1);
}
private int contains(int key){
for (int i = 0; i < entries.size(); i++) {
if (entries.get(i).k == key){
return i;
}
}
return -1;
}
}
NC4 判断链表中是否有环
https://www.nowcoder.com/practice/650474f313294468a4ded3ce0f7898b9
public class Solution {
public boolean hasCycle(ListNode head) {
ListNode slow = head;
ListNode fast = head;
while(fast != null && fast.next != null){
fast = fast.next.next;
slow = slow.next;
if(fast == slow) return true;
}
return false;
}
}
NC105 二分查找-II
public class Solution {
/**
* 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
*
* 如果目标值存在返回下标，否则返回 -1
* @param nums int整型一维数组
* @param target int整型
* @return int整型
*/
public int search (int[] nums, int target) {
int begin = 0;
int end = nums.length - 1;
int med = 0;
while(begin <= end){
if(nums[begin] == target) return begin;
med = (begin + end) / 2;
if(nums[med] > target){
end = med - 1;
}else if(nums[med] < target){
begin = med + 1;
}else{
if(med == 0 || nums[med - 1] != target) return med;
begin++;
}
}
return -1;
}
}
NC15 求二叉树的层序遍历
https://www.nowcoder.com/practice/04a5560e43e24e9db4595865dc9c63a3
import java.util.*;
/*
* public class TreeNode {
* int val = 0;
* TreeNode left = null;
* TreeNode right = null;
* }
*/
public class Solution {
/**
*
* @param root TreeNode类
* @return int整型ArrayList<ArrayList<>>
*/
public ArrayList<ArrayList<Integer>> levelOrder (TreeNode root) {
ArrayList<ArrayList<Integer>> result = new ArrayList<>();
if(root == null) return result;
Queue<TreeNode> q1 = new LinkedList<>();
Queue<TreeNode> q2 = new LinkedList<>();
q1.offer(root);
while(!q1.isEmpty() || !q2.isEmpty()){
ArrayList<Integer> list = new ArrayList<>();
while(!q1.isEmpty()){
TreeNode poll = q1.poll();
list.add(poll.val);
if(poll.left != null){
q2.offer(poll.left);
}
if(poll.right != null){
q2.offer(poll.right);
}
}
if(!list.isEmpty())
result.add(list);
list = new ArrayList<>();
while(!q2.isEmpty()){
TreeNode poll = q2.poll();
list.add(poll.val);
if(poll.left != null){
q1.offer(poll.left);
}
if(poll.right != null){
q1.offer(poll.right);
}
}
if(!list.isEmpty())
result.add(list);
}
return result;
}
}
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