Array：
Single Number
1 class Solution { 2 public int singleNumber(int[] nums) { 3 if (nums == null || nums.length == 0) { 4 return 0; 5 } 6 int res = nums[0]; 7 for (int i = 1; i < nums.length; i++) { 8 res = res ^ nums[i]; 9 }10 11 return res;12 }13 } Remove Duplicates from Sorted Array
1 class Solution { 2 public int removeDuplicates(int[] nums) { 3 if(nums==null || nums.length==0){ 4 return 0; 5 } 6 int res =1; 7 for(int i=1;i Best Time to Buy and Sell Stock II
1 class Solution { 2 public int maxProfit(int[] prices) { 3 if (prices == null || prices.length == 0) { 4 return 0; 5 } 6 int res = 0; 7 for (int i = 0; i < prices.length - 1; i++) { 8 if (prices[i + 1] - prices[i] > 0) { 9 res += prices[i + 1] - prices[i];10 }11 }12 return res;13 }14 } Rotate Array
这题注意处理k>nums.length的情况，直接取余
1 class Solution { 2 public void rotate(int[] nums, int k) { 3 if (nums == null || nums.length == 0) { 4 return; 5 } 6 k = k%nums.length; 7 rotateSubArray(nums, 0, nums.length - k - 1); 8 rotateSubArray(nums, nums.length - k, nums.length - 1); 9 rotateSubArray(nums, 0, nums.length - 1);10 }11 12 public void rotateSubArray(int[] nums, int start, int end) {13 int left = start;14 int right = end;15 while (left < right) {16 swap(nums, left, right);17 left++;18 right--;19 }20 }21 22 public void swap(int[] nums, int aIndex, int bIndex) {23 int temp = nums[aIndex];24 nums[aIndex] = nums[bIndex];25 nums[bIndex] = temp;26 }27 } Contains Duplicate
1 class Solution { 2 public boolean containsDuplicate(int[] nums) { 3 if (nums == null || nums.length == 0) { 4 return false; 5 } 6 7 Arrays.sort(nums); 8 for (int i = 0; i < nums.length - 1; i++) { 9 if (nums[i] == nums[i + 1])10 return true;11 }12 13 return false;14 }15 } Intersection of Two Arrays II
1 class Solution { 2 public int[] intersect(int[] nums1, int[] nums2) { 3 if (nums1 == null || nums1.length == 0) { 4 return nums1; 5 } 6 7 if (nums2 == null || nums2.length == 0) { 8 return nums2; 9 }10 List list = new ArrayList<>();11 HashMap map = new HashMap<>();12 for (int num : nums1) {13 if (map.get(num) == null) {14 map.put(num, 1);15 } else {16 map.put(num, map.get(num) + 1);17 }18 }19 20 for (int num : nums2) {21 Integer exist = map.get(num);22 if (exist != null && exist > 0) {23 map.put(num, exist - 1);24 list.add(num);25 }26 }27 28 int[] res = new int[list.size()];29 for (int i = 0; i < res.length; i++) {30 res[i] = list.get(i);31 }32 return res;33 }34 } Plus One
注意当结果为1000...时需重新生成长数组返回，否则WA(eg：99999 -> 00000)
1 class Solution { 2 public int[] plusOne(int[] digits) { 3 if (digits == null || digits.length == 0) { 4 return digits; 5 } 6 7 int carry = digits[digits.length - 1] + 1 >= 10 ? 1 : 0; 8 digits[digits.length - 1] = carry == 1 ? 0 : digits[digits.length - 1] + 1; 9 if (carry == 0) {10 return digits;11 }12 for (int i = digits.length - 2; i >= 0; i--) {13 if (digits[i] + carry >= 10) {14 digits[i] = 0;15 } else {16 digits[i] = digits[i] + carry;17 return digits;18 }19 }20 21 int[] newNumber = new int[digits.length+1];22 newNumber[0] = 1;23 return newNumber;24 }25 } Move Zeroes
1 class Solution { 2 public void moveZeroes(int[] nums) { 3 if (nums == null || nums.length == 0) { 4 return; 5 } 6 7 int noZeroIndex = 0; 8 for (int i = 0; i < nums.length; i++) { 9 if (nums[i] != 0) {10 nums[noZeroIndex] = nums[i];11 noZeroIndex++;12 }13 }14 15 for (int j = noZeroIndex; j < nums.length; j++) {16 nums[j] = 0;17 }18 19 return;20 }21 } Two Sum
1 class Solution { 2 public int[] twoSum(int[] nums, int target) { 3 if (nums == null || nums.length < 2) { 4 return null; 5 } 6 7 Map map = new HashMap<>(); 8 for (int i = 0; i < nums.length; i++) { 9 Integer exist = map.get(target - nums[i]);10 if (exist != null) {11 int[] res = new int[2];12 res[0] = i;13 res[1] = exist;14 return res;15 }16 map.put(nums[i], i);17 }18 19 return null;20 }21 }
Strings
Reverse String
1 class Solution { 2 public String reverseString(String s) { 3 if (s == null || s.length() == 0) { 4 return s; 5 } 6 char[] arrays = s.toCharArray(); 7 int start = 0; 8 int end = arrays.length - 1; 9 while (start < end) {10 char temp = arrays[start];11 arrays[start] = arrays[end];12 arrays[end] = temp;13 start++;14 end--;15 }16 17 return new String(arrays);18 }19 } Reverse Integer
1 class Solution { 2 public int reverse(int x) { 3 String s = x + ""; 4 if (s.length() <= 1) { 5 return x; 6 } 7 char[] arrays = s.toCharArray(); 8 int len = arrays.length; 9 int start = 0;10 int end = s.length() - 1;11 while (start < arrays.length && arrays[start] > '9' || arrays[start] < '0') {12 start++;13 }14 while (end >= 0 && arrays[end] == '0') {15 arrays[end] = ' ';16 end--;17 }18 while (start < end) {19 char temp = arrays[start];20 arrays[start] = arrays[end];21 arrays[end] = temp;22 start++;23 end--;24 }25 26 s = new String(arrays);27 Long res = Long.valueOf(s.trim());28 if (res > Integer.MAX_VALUE || res < Integer.MIN_VALUE) {29 return 0;30 }31 return res.intValue();32 }33 } First Unique Character in a String
1 class Solution { 2 public int firstUniqChar(String s) { 3 if (s == null || s.length() == 0) { 4 return -1; 5 } 6 7 char[] array = s.toCharArray(); 8 Map map = new HashMap<>(); 9 for (int i = 0; i < array.length; i++) {10 Integer exist = map.get(array[i]);11 if (exist == null) {12 map.put(array[i], 1);13 } else {14 map.put(array[i], exist + 1);15 }16 }17 18 for (int i = 0; i < array.length; i++) {19 if (map.get(array[i]) == 1) {20 return i;21 }22 }23 return -1;24 }25 } Valid Palindrome
1 class Solution { 2 public boolean isPalindrome(String s) { 3 if (s == null || s.length() == 0) { 4 return true; 5 } 6 s = s.trim(); 7 int start = 0; 8 int end = s.length() - 1; 9 while (start < end) {10 while (start < s.length() && !Character.isLetter(s.charAt(start)) && !Character.isDigit(s.charAt(start))) {11 start++;12 }13 14 while (end >= 0 && !Character.isLetter(s.charAt(end)) && !Character.isDigit(s.charAt(end))) {15 end--;16 }17 if (start >= end) {18 break;19 }20 if (Character.toLowerCase(s.charAt(start)) != Character.toLowerCase(s.charAt(end))) {21 return false;22 }23 start++;24 end--;25 }26 27 return true;28 }29 }