[8/9] M19/M22/M24/M31/M33/M34/M36

[8/9] M19/M22/M24/M31/M34

M19. Remove Nth Node From End of List

用时：20 mins

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public ListNode removeNthFromEnd(ListNode head, int n) {ListNode dummy =  new ListNode();dummy.next = head;ListNode first = dummy, second = dummy;int firstCount = 0, secondCount = 0;while(first.next != null) {first = first.next;firstCount++;if(firstCount >= n+1) {second = second.next;secondCount++;}}if(second.next != null) {ListNode toRemove = second.next;second.next = toRemove.next;}return dummy.next;}
}

M22. Generate Parentheses

用时：20 mins

class Solution {List<String> res = new ArrayList<>();public List<String> generateParenthesis(int n) {backTracking("", 0, 0, n);return res;}public void backTracking(String str, int open, int close, int max){if(str.length() == max*2) {res.add(str);return;} if(open<max) {backTracking(str+"(", open+1, close, max);}if(close<open) {backTracking(str+")", open, close+1, max);}}
}

M24. Swap Nodes in Pairs

用时： 15 mins
24. Swap Nodes in Pairs

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public ListNode swapPairs(ListNode head) {if(head == null) return head;ListNode dummy = new ListNode();dummy.next = head;ListNode previous = dummy, next = null;ListNode first = head, second = head.next;while(first != null && second != null) {next = second.next;previous.next = second;second.next = first;first.next = next;if (first.next == null || first.next.next == null) break;previous = first; first = previous.next;second = first.next;}return dummy.next;}
}

M31. Next Permutation

class Solution {public void nextPermutation(int[] nums) {for (int i = nums.length -2; i>=0; i--) {if(nums[i+1] > nums[i]) {for(int j = nums.length -1; j>i; j--) {if (nums[j] > nums[i]) {swap(nums, i, j);reverse(nums, i+1);return;}}}}reverse(nums, 0);}public void swap(int[] nums, int i, int j) {int toSwap = nums[i];nums[i] = nums[j];nums[j] = toSwap;}public void reverse(int[] nums, int start){int i = start, j = nums.length-1;while(i<j) {swap(nums, i, j);i++;j--;}}
}

M33. Search in Rotated Sorted Array

class Solution {public int search(int[] nums, int target) {int start = 0, end = nums.length -1, mid = 0;while (start<=end) {mid = start + (end - start)/2;if(nums[mid] == target) return mid;if (nums[start] <= nums[mid]) {if( target <= nums[mid] && target >= nums[start]) {end = mid-1;} else {start = mid+1;}} else {if(target <= nums[end] && target >= nums[mid]) {start = mid+1;} else {end = mid -1; }}}return -1;}
}

M34. Find First and Last Position of Element in Sorted Array

class Solution {int[] res = new int[2];int rangeStart = -1, rangeEnd = -1;public int[] searchRange(int[] nums, int target) {int start = 0, end = nums.length -1, mid = 0; recurse(nums, target, start, end);res[0] = rangeStart;res[1] = rangeEnd;return res;}public void recurse(int[] nums, int target, int start, int end) {if (start<end) {int mid = start + (end -start)/2;if(nums[mid] == target) {recurse(nums, target, start, mid-1);recurse(nums, target, mid + 1, end);setValue(mid);} else if (target < nums[mid]){recurse(nums, target, start, mid-1);} else if (target > nums[mid]){recurse(nums, target, mid + 1, end);}} else if(start==end && nums[start] == target) {setValue(start);}}private void setValue(int val) {if(rangeStart != -1) {rangeStart = Math.min(val, rangeStart);} else {rangeStart = val;}rangeEnd = Math.max(val, rangeEnd);}
}

M36. Valid Sudoku

public class Solution {public boolean isValidSudoku(char[][] board) {HashMap<Integer, Integer> [] rows = new HashMap[9];HashMap<Integer, Integer> [] columns = new HashMap[9];HashMap<Integer, Integer> [] boxes = new HashMap[9];for(int i = 0; i<9; i++) {rows[i] = new HashMap<Integer, Integer>();columns[i] = new HashMap<Integer, Integer>();boxes[i] = new HashMap<Integer, Integer>();}for(int i = 0; i<9; i++) {for(int j = 0; j<9; j++) {char num = board[i][j];if (num == '.') continue;System.out.println("num:"+num + ":");int n = (int)num;rows[i].put(n, rows[i].getOrDefault(n, 0) + 1);columns[j].put(n, columns[j].getOrDefault(n, 0) + 1);System.out.println(":"+n + ":");System.out.println(columns[j].get(n));int boxIndex = (i/3) * 3 + (j/3);boxes[boxIndex].put(n, boxes[boxIndex].getOrDefault(n, 0) + 1);if(rows[i].get(n) >1 || columns[j].get(n) > 1 || boxes[boxIndex].get(n) >1) return false;}}return true;}
}

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[8/9] M19/M22/M24/M31/M33/M34/M36

[8/9] M19/M22/M24/M31/M34

M19. Remove Nth Node From End of List

M22. Generate Parentheses

M24. Swap Nodes in Pairs

M31. Next Permutation

M33. Search in Rotated Sorted Array

M34. Find First and Last Position of Element in Sorted Array

M36. Valid Sudoku

[8/9] M19/M22/M24/M31/M33/M34/M36相关推荐

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