同向双指针：
100. Remove Duplicates from Sorted Array
1 public class Solution {
2 /*
3 * @param nums: An ineger array
4 * @return: An integer
5 */
6 public int removeDuplicates( int [] nums) {
7 // write your code here
8
9 if (nums == null ||nums.length ==0 ){
10 return 0 ;
11 }
12
13 int index=0 ;
14 for ( int i=0; i<nums.length;i++){
15 if (i==0 || nums[i]!=nums[i-1 ]){
16 nums[index]= nums[i];
17 index++ ;
18 }
19 }
20
21 return index;
22 }
23 }
539. Move Zeroes
1 public class Solution {
2 /**
3 * @param nums: an integer array
4 * @return: nothing
5 */
6 public void moveZeroes(int[] nums) {
7 // write your code here
8 if (nums == null || nums.length == 0) {
9 return;
10 }
11
12 int zeroIndex = 0;
13 int numIndex = 0;
14 while (zeroIndex < nums.length) {
15 if (nums[zeroIndex] != 0) {
16 swap(nums, zeroIndex, numIndex);
17 numIndex++;
18 }
19 zeroIndex++;
20 }
21 }
22
23 public void swap(int[] num, int left, int right) {
24 int temp = num[left];
25 num[left] = num[right];
26 num[right] = temp;
27 }
28 }
604. Window Sum
1 public class Solution {
2 /**
3 * @param nums: a list of integers.
4 * @param k: length of window.
5 * @return: the sum of the element inside the window at each moving.
6 */
7 public int[] winSum(int[] nums, int k) {
8 // write your code here
9 if (nums == null || nums.length == 0 || k > nums.length) {
10 return new int[0];
11 }
12
13 int len = nums.length - k + 1;
14 int[] res = new int[len];
15
16 for (int i = 0; i < k; i++) {
17 res[0] += nums[i];
18 }
19
20 for (int j = 1; j < res.length; j++) {
21 res[j] = res[j - 1] - nums[j - 1] + nums[j + k - 1];
22 }
23 return res;
24 }
25 }
相向双指针：
415. Valid Palindrome
1 public class Solution {
2 /**
3 * @param s: A string
4 * @return: Whether the string is a valid palindrome
5 */
6 public boolean isPalindrome(String s) {
7 // write your code here
8 if (s == null || s.length() == 0) {
9 return true;
10 }
11
12 int start = 0;
13 int end = s.length() - 1;
14 while (start < end) {
15 while (start < end && !isCharacter(s.charAt(start))) {
16 start++;
17 }
18
19 while (start < end && !isCharacter(s.charAt(end))) {
20 end--;
21 }
22
23 if (Character.toLowerCase(s.charAt(start)) != Character.toLowerCase(s.charAt(end))) {
24 return false;
25 }
26 start++;
27 end--;
28 }
29 return true;
30 }
31
32 public boolean isCharacter(char c) {
33 return Character.isLetter(c) || Character.isDigit(c);
34 }
35 }
8. Rotate String
三步翻转
1 public class Solution {
2 /**
3 * @param str: An array of char
4 * @param offset: An integer
5 * @return: nothing
6 */
7 public void rotateString(char[] str, int offset) {
8 // write your code here
9 if (str == null || str.length == 0 || offset == 0) {
10 return;
11 }
12
13 int k = offset % str.length;
14 reverse(str, 0, str.length - k - 1);
15 reverse(str, str.length - k, str.length-1);
16 reverse(str, 0, str.length - 1);
17 return;
18 }
19
20 public void reverse(char[] str, int start, int end) {
21 while (start < end) {
22 char temp = str[start];
23 str[start] = str[end];
24 str[end] = temp;
25 start++;
26 end--;
27 }
28 }
29 }
39. Recover Rotated Sorted Array
找到翻转点，思路同上
1 public class Solution {
2 /**
3 * @param nums: An integer array
4 * @return: nothing
5 */
6 public void recoverRotatedSortedArray(List<Integer> nums) {
7 // write your code here
8 if (nums == null || nums.size() == 0) {
9 return;
10 }
11 for (int i = 0; i < nums.size() - 1; i++) {
12 if (nums.get(i) > nums.get(i + 1)) {
13 reverse(nums, 0, i);
14 reverse(nums, i + 1, nums.size() - 1);
15 reverse(nums, 0, nums.size() - 1);
16 return;
17 }
18 }
19
20 }
21
22 public void reverse(List<Integer> nums, int start, int end) {
23 while (start < end) {
24 int temp = nums.get(start);
25 nums.set(start, nums.get(end));
26 nums.set(end, temp);
27 start++;
28 end--;
29 }
30 }
31 }
607. Two Sum III - Data structure design
1 public class TwoSum {
2 /**
3 * @param number: An integer
4 * @return: nothing
5 */
6 private Map<Integer, Integer> map = new HashMap<>();
7
8 public void add(int number) {
9 // write your code here
10 if (map.containsKey(number)) {
11 map.put(number, map.get(number) + 1);
12 return;
13 }
14 map.put(number, 1);
15 }
16
17 /**
18 * @param value: An integer
19 * @return: Find if there exists any pair of numbers which sum is equal to the value.
20 */
21 public boolean find(int value) {
22 // write your code here
23 for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
24 if (value - entry.getKey() == entry.getKey()) {
25 if (entry.getValue() > 1) {
26 return true;
27 }
28 continue;
29 }
30 Integer targetIndex = map.get(value - entry.getKey());
31 if (targetIndex != null) {
32 return true;
33 }
34 }
35 return false;
36 }
37 }
608. Two Sum II - Input array is sorted
1 public class Solution {
2 /**
3 * @param nums: an array of Integer
4 * @param target: target = nums[index1] + nums[index2]
5 * @return: [index1 + 1, index2 + 1] (index1 < index2)
6 */
7 public int[] twoSum(int[] nums, int target) {
8 // write your code here
9 int[] res = new int[2];
10 if (nums == null || nums.length == 0) {
11 return res;
12 }
13 int start = 0;
14 int end = nums.length - 1;
15 while (start < end) {
16 int sum = nums[start] + nums[end];
17 if (sum == target) {
18 res[0] = start + 1;
19 res[1] = end + 1;
20 return res;
21 }
22 if (sum > target) {
23 end--;
24 }
25 if (sum < target) {
26 start++;
27 }
28 }
29 return res;
30 }
31 }
587. Two Sum - Unique pairs
1 public class Solution {
2 public int twoSum(int[] nums, int target) {
3 // write your code here
4 if (nums == null || nums.length == 0) {
5 return 0;
6 }
7 Arrays.sort(nums);
8 int start = 0;
9 int end = nums.length - 1;
10 int count = 0;
11 while (start < end) {
12 int sum = nums[start] + nums[end];
13 if (sum == target) {
14 count++;
15 start++;
16 end--;
17 while (start < end && nums[start] == nums[start - 1]) start++;
18 while (start < end && nums[end] == nums[end + 1]) end--;
19 }
20 if (sum > target) {
21 end--;
22 }
23 if (sum < target) {
24 start++;
25 }
26 }
27 return count;
28 }
29 }
57. 3Sum
1 public class Solution {
2 /**
3 * @param numbers: Give an array numbers of n integer
4 * @return: Find all unique triplets in the array which gives the sum of zero.
5 */
6 public List<List<Integer>> threeSum(int[] numbers) {
7 // write your code here
8 List<List<Integer>> res = new ArrayList<>();
9 if (numbers == null || numbers.length < 3) {
10 return res;
11 }
12
13 Arrays.sort(numbers);
14 for (int i = 0; i < numbers.length - 2; i++) {
15 if (i > 0 && numbers[i] == numbers[i - 1]) continue;
16 towSum(numbers, i + 1, numbers.length - 1, 0 - numbers[i], res);
17 }
18 return res;
19 }
20
21 public void towSum(int[] numbers, int start, int end, int target, List<List<Integer>> res) {
22 while (start < end) {
23 int sum = numbers[start] + numbers[end];
24 if (sum == target) {
25 List<Integer> pair = new ArrayList<>();
26 pair.add(-target);
27 pair.add(numbers[start]);
28 pair.add(numbers[end]);
29 res.add(pair);
30 start++;
31 end--;
32 while (start < end && numbers[start] == numbers[start - 1]) start++;
33 while (start < end && numbers[end] == numbers[end + 1]) end--;
34 }
35 if (sum > target) {
36 end--;
37 }
38 if (sum < target) {
39 start++;
40 }
41
42 }
43 }
44
45 }
382. Triangle Count
1 public class Solution {
2 /**
3 * @param S: A list of integers
4 * @return: An integer
5 */
6 public int triangleCount(int[] S) {
7 // write your code here
8 if (S == null || S.length < 3) {
9 return 0;
10 }
11 Arrays.sort(S);
12 int count = 0;
13 for (int i = 2; i < S.length; i++) {
14 int left = 0;
15 int right = i - 1;
16 while (left < right) {
17 int sum = S[left] + S[right];
18 if (sum > S[i]) {
19 count += right - left;
20 right--;
21 }
22 if (sum <= S[i]) {
23 left++;
24 }
25 }
26 }
27
28 return count;
29 }
30 }
59. 3Sum Closest
1 public class Solution {
2 /**
3 * @param numbers: Give an array numbers of n integer
4 * @param target: An integer
5 * @return: return the sum of the three integers, the sum closest target.
6 */
7 public int threeSumClosest(int[] numbers, int target) {
8 // write your code here
9 if (numbers == null || numbers.length < 3) {
10 return 0;
11 }
12 Arrays.sort(numbers);
13 int res = numbers[0] + numbers[1] + numbers[2];
14 for (int i = 0; i < numbers.length; i++) {
15 int start = i + 1;
16 int end = numbers.length - 1;
17 int num = numbers[i];
18 while (start < end) {
19 int sum = numbers[start] + numbers[end] + num;
20 if (Math.abs(sum - target) < Math.abs(res - target)) {
21 res = sum;
22 }
23 if (sum == target) {
24 return target;
25 }
26 if (sum > target) {
27 end--;
28 }
29 if (sum < target) {
30 start++;
31 }
32 }
33 }
34 return res;
35 }
36
37 }
31. Partition Array(需重刷)
1 public class Solution {
2 /**
3 *@param nums: The integer array you should partition
4 *@param k: As description
5 *return: The index after partition
6 */
7 public int partitionArray(int[] nums, int k) {
8 if(nums == null || nums.length == 0){
9 return 0;
10 }
11
12 int left = 0, right = nums.length - 1;
13 while (left <= right) {
14
15 while (left <= right && nums[left] < k) {
16 left++;
17 }
18
19 while (left <= right && nums[right] >= k) {
20 right--;
21 }
22
23 if (left <= right) {
24 int temp = nums[left];
25 nums[left] = nums[right];
26 nums[right] = temp;
27
28 left++;
29 right--;
30 }
31 }
32 return left;
33 }
34 }
373. Partition Array by Odd and Even
1 public class Solution {
2 /*
3 * @param nums: an array of integers
4 * @return: nothing
5 */
6 public void partitionArray(int[] nums) {
7 // write your code here
8 if (nums == null || nums.length == 0) {
9 return;
10 }
11 int left = 0;
12 int right = nums.length - 1;
13
14 while (left <= right) {
15 while (left <= right && nums[left] % 2 == 1) {
16 left++;
17 }
18
19 while (left <= right && nums[right] % 2 == 0) {
20 right--;
21 }
22 if (left <= right) {
23 int temp = nums[left];
24 nums[left] = nums[right];
25 nums[right] = temp;
26 left++;
27 right--;
28 }
29 }
30 return;
31
32 }
33 }
49. Sort Letters by Case
1 public class Solution {
2 /*
3 * @param chars: The letter array you should sort by Case
4 * @return: nothing
5 */
6 public void sortLetters(char[] chars) {
7 // write your code here
8 if (chars == null || chars.length == 0) {
9 return;
10 }
11
12 int start = 0;
13 int end = chars.length - 1;
14 while (start <= end) {
15 while (start <= end && Character.isLowerCase(chars[start])) start++;
16 while (start <= end && !Character.isLowerCase(chars[end])) end--;
17 if (start <= end) {
18 char temp = chars[start];
19 chars[start] = chars[end];
20 chars[end] = temp;
21 start++;
22 end--;
23 }
24 }
25 return;
26 }
27 }
148. Sort Colors
1 public class Solution {
2 /**
3 * @param nums: A list of integer which is 0, 1 or 2
4 * @return: nothing
5 */
6 public void sortColors(int[] nums) {
7 // write your code here
8 if (nums == null || nums.length == 0) return;
9
10 int left = 0;
11 int right = nums.length - 1;
12 int i = 0;
13
14 while (i <= right) {
15 if (nums[i] == 0) {
16 int temp = nums[i];
17 nums[i] = nums[left];
18 nums[left] = temp;
19 left++;
20 i++;
21 }
22 else if (nums[i] == 1) {
23 i++;
24 }
25 else {
26 int temp = nums[i];
27 nums[i] = nums[right];
28 nums[right] = temp;
29 right--;
30 }
31 }
32 return;
33 }
34 }
143. Sort Colors II（148的FollowUp）快排和归并排序的结合
1 public class Solution {
2 /**
3 * @param colors: A list of integer
4 * @param k: An integer
5 * @return: nothing
6 */
7 public void sortColors2(int[] colors, int k) {
8 // write your code here
9 if (colors == null || colors.length == 0 || k > colors.length) {
10 return;
11 }
12
13 partitionColor(colors, 0, colors.length - 1, 0, k);
14 }
15
16 //start-end 排序的数组起始下标
17 //colorFrom-colorTo 这一段的颜色
18 public void partitionColor(int[] colors, int startIndex, int endIndex, int colorFrom, int colorTo) {
19 if (colorFrom == colorTo)
20 return;
21 if (startIndex > endIndex) {
22 return;
23 }
24 int left = startIndex;
25 int right = endIndex;
26 //划分的颜色
27 int colorMid = colorFrom + (colorTo - colorFrom) / 2;
28 while (left <= right) {
29 while (left <= right && colors[left] <= colorMid) left++;
30 while (left <= right && colors[right] > colorMid) right--;
31 if (left <= right) {
32 int temp = colors[left];
33 colors[left] = colors[right];
34 colors[right] = temp;
35 left++;
36 right--;
37 }
38 }
39 partitionColor(colors, startIndex, right, colorFrom, colorMid);
40 partitionColor(colors, left, endIndex, colorMid + 1, colorTo);
41 }
42 }
原文地址：https://www.cnblogs.com/lizzyluvcoding/p/9721031.html
时间： 2024-11-13 02:59:19