leetcode-數組篇
Posted 小傻孩、儿
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Remove Element
public class Lc27 { public static int removeElement(int[] nums, int val) { if (nums == null || nums.length == 0) { return 0; } int count = 0; for (int i = 0; i < nums.length;) { if (nums[i] == val) { count++; move(nums, i); } else { i++; } } return nums.length - count; } public static void move(int[] nums, int position) { for (int i = position; i < nums.length - 1; i++) { nums[i] = nums[i + 1]; } nums[nums.length - 1] = Integer.MAX_VALUE; } public static void main(String[] args) { int[] nums = { 0, 1, 2, 2, 3, 0, 4, 2 }; int val = 2; System.out.println(removeElement(nums, val)); } }
Remove Duplicates from Sorted Array,这里用了六种排序,由于题目中有负数导致基数排序可能会出现数组下标错误
import java.util.ArrayList; import java.util.List; /** * 俩个排序算法 * */ public class Lc26 { public static int removeDuplicates(int[] nums) { int count = 0; for (int i = 0; i < nums.length - 1; i++) { if (nums[i] == nums[i + 1]) { nums[i] = Integer.MAX_VALUE; count++; } } // nums = insertSort(nums); // nums = shellSort(nums); // nums = selectSort(nums); // nums = bubbleSort(nums); // quickSort(nums, 0, nums.length - 1); nums = radixSort(nums); return nums.length - count; } /** * 插入排序,遍历所有的元素和以前排好的元素,如果选择的元素比以前的元素小就替换。 */ public static int[] insertSort(int[] nums) { for (int i = 1; i < nums.length; i++) { for (int j = 0; j < i; j++) { if (nums[i] < nums[j]) { int temp = nums[i]; nums[i] = nums[j]; nums[j] = temp; break; } } } return nums; } /** * 插入排序,遍历所有的元素和以前排好的元素,如果选择的元素比以前的元素小就替换。 希尔排序:在插入排序的基础上增加控制增量,逻辑分组数据,每次比较俩端数据 */ public static int[] shellSort(int[] nums) { for (int gap = nums.length / 2; gap > 0; gap /= 2) { for (int i = gap; i < nums.length; i++) { for (int j = i; j >= gap; j -= gap) { if (nums[j] < nums[j - gap]) { int temp = nums[j]; nums[j] = nums[j - gap]; nums[j - gap] = temp; } } } } return nums; } /** * 选择排序:再要排序中的数组中,选出最小的数字和第一个数字替换,一次选出第二小的数组和第二个数字替换,一次类推 */ public static int[] selectSort(int[] nums) { for (int i = 0; i < nums.length; i++) { int index = nums[i]; for (int j = i + 1; j < nums.length; j++) { if (nums[j] < nums[i]) { int temp = nums[j]; nums[j] = nums[i]; nums[i] = temp; } } } return nums; } /* * 冒泡排序:对当前还未排好顺序的元素进行自顶向下排序,交换相邻的俩个数字,小数上浮,大数下沉 */ public static int[] bubbleSort(int[] nums) { for (int i = 0; i < nums.length; i++) { for (int j = i + 1; j < nums.length; j++) { if (nums[j] < nums[i]) { int temp = nums[j]; nums[j] = nums[i]; nums[i] = temp; } } } return nums; } /** * 快速排序:选取一个基准值,利用二分法对其排序 */ public static void quickSort(int[] nums, int low, int hign) { if (low < hign) { int index = getIndex(nums, low, hign); quickSort(nums, 0, index - 1); quickSort(nums, index + 1, hign); } } private static int getIndex(int[] nums, int low, int hign) { int temp = nums[low]; while (low < hign) { while (low < hign && nums[hign] >= temp) { hign--; } nums[low] = nums[hign]; while (low < hign && nums[low] <= temp) { low++; } nums[hign] = nums[low]; } nums[low] = temp; return low; } /** * 基数排序:低位优先,比较每个数字的低位,依次到高位,注意是正整数 */ public static int[] radixSort(int[] nums) { if (nums == null || nums.length == 0) { return nums; } int max = nums[0]; for (int i = 0; i < nums.length; i++) { if (max < nums[i]) { max = nums[i]; } } int digit = 0; while (max != 0) { max /= 10; digit++; } // init list List<List<Integer>> buckets = new ArrayList<List<Integer>>(); for (int i = 0; i < 10; i++) { buckets.add(new ArrayList<>()); } for (int i = 0; i < digit; i++) { for (int j = 0; j < nums.length; j++) { int key = (int) (nums[j] % Math.pow(10, i + 1) / Math.pow(10, i)); buckets.get(key).add(nums[j]); } int count = 0; for (int j = 0; j < nums.length; j++) { while (buckets.get(j).size() > 0) { nums[count++] = buckets.get(j).remove(0); } } // 分配完之后,将桶中的元素依次复制回数组 } return nums; } public static void main(String[] args) { int[] nums = { -1, 0, 0, 0, 0, 3, 3 }; System.out.println(removeDuplicates(nums)); } }
Remove Duplicates from Sorted Array II
import java.util.Arrays; import java.util.HashMap; import java.util.Map; public class Lc80 { public static int removeDuplicates(int[] nums) { // map(数字/次数) Map<Integer, Integer> map = new HashMap<Integer, Integer>(); int count = 0; for (int i = 0; i < nums.length; i++) { if (map.containsKey(nums[i])) { int temp = map.get(nums[i]); if (temp >= 2) { count++; nums[i] = Integer.MAX_VALUE; } else { map.put(nums[i], ++temp); } } else { map.put(nums[i], 1); } } Arrays.sort(nums); return nums.length - count; } public static void main(String[] args) { int[] nums = { 1, 1, 1 }; System.out.println(removeDuplicates(nums)); } }
Find the Celebrity
Rotate Array
public class Lc189 { public static void rotate(int[] nums, int k) { int previous = 0; for (int i = 0; i < k; i++) { previous = nums[nums.length - 1]; for (int j = 0; j < nums.length; j++) { int temp = previous; previous = nums[j]; nums[j] = temp; } } } public static void main(String[] args) { int[] nums = { 1, 2, 3, 4, 5, 6, 7 }; int k = 3; rotate(nums, k); } }
First Missing Positive
import java.util.Arrays; import java.util.HashMap; import java.util.Map; public class Lc41 { public static int firstMissingPositive(int[] nums) { Map<Integer, Integer> map = new HashMap<Integer, Integer>(); for (int i = 0; i < nums.length; i++) { if (map.containsKey(nums[i])) { nums[i] = Integer.MAX_VALUE; } else { map.put(nums[i], i); } } Arrays.sort(nums); int min = 0; int minPosition = 0; for (int i = 0; i < nums.length; i++) { if (nums[i] > 0) { minPosition = i; min = nums[i]; break; } } if (min != 1) { return 1; } int j = 1; for (int i = minPosition; i < nums.length; i++, j++) { if (nums[i] != j) { return j; } } return j; } public static void move(int[] nums, int position) { for (int i = 0; i < nums.length - 1; i++) { nums[i] = nums[i + 1]; } nums[nums.length - 1] = Integer.MAX_VALUE; } public static void main(String[] args) { int[] nums = { 0, 2, 2, 1, 1 }; System.out.println(firstMissingPositive(nums)); } }
Bulls and Cows
import java.util.ArrayList; import java.util.List; public class Lc229 { public static String getHint(String secret, String guess) { int bulls = 0; int cows = 0; List<String> secretDigits = convertToAscall(secret); List<String> guessDigits = convertToAscall(guess); for (int i = 0; i < secretDigits.size(); i++) { if (secretDigits.get(i).equals(guessDigits.get(i))) { bulls++; } else { cows++; } } return bulls + "A" + cows + "B"; } private static List<String> convertToAscall(String s) { StringBuffer sb = new StringBuffer(); char[] chars = s.toCharArray(); for (char c : chars) { sb.append((int) c).append(","); } String[] str = sb.toString().split(","); List<String> lists = new ArrayList<>(); for (String string : str) { lists.add(string); } return lists; } public static void main(String[] args) { String secret = "1123"; String guess = "0111"; System.out.println(getHint(secret, guess)); } }
参考文档:https://cspiration.com/leetcodeClassification#10309
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