JZ53 数字在升序数组中出现的次数⭐
1 /* 二分左边界 */
2 public class JZ53_1
3 {
4 public static int GetNumberOfK(int[] nums, int k)
5 {
6 int left = 0, right = nums.length - 1, mid = -1, res = 0;
7 while (left <= right)
8 {
9 mid = (left + right) / 2;
10 if (nums[mid] >= k) right = mid - 1;
11 else left = mid + 1;
12 }
13 for (right++; right < nums.length && nums[right] == k; right++)
14 res++;
15 return res;
16 }
17 }
18
19 /* 二分右边界 */
20 public class JZ53_2
21 {
22 public static int GetNumberOfK(int[] nums, int k)
23 {
24 int left = 0, right = nums.length - 1, mid = -1, res = 0;
25 while (left <= right)
26 {
27 mid = (left + right) / 2;
28 if (nums[mid] <= k) left = mid + 1;
29 else right = mid - 1;
30 }
31 for (left--; left >= 0 && nums[left] == k; left--)
32 res++;
33 return res;
34 }
35 }
JZ4 二维数组中的查找⭐
1 /* 从左下角出发，每次排除一行或一列 */
2 public class JZ4_1
3 {
4 public static boolean Find(int target, int[][] array)
5 {
6 int i = array.length - 1, j = 0;
7 while (true)
8 {
9 if (i < 0 || j > array[0].length - 1) return false;
10 if (array[i][j] == target) return true;
11 else if (array[i][j] > target) i--;
12 else j++;
13 }
14 }
15 }
16
17 /* 递归 */
18 public class JZ4_2
19 {
20 public static boolean Find(int target, int[][] array)
21 {
22 return find(0, 0, array.length - 1, array[0].length - 1, target, array);
23 }
24
25 public static boolean find(int topLeftX, int topLeftY, int lowRightX, int lowRightY, int target, int[][] array)
26 {
27 if (topLeftX < 0 || topLeftX >= array.length || topLeftY < 0 || topLeftY >= array[0].length) return false;
28 if (lowRightX < 0 || lowRightX >= array.length || lowRightY < 0 || lowRightY >= array[0].length) return false;
29 if (topLeftX > lowRightX || topLeftY > lowRightY) return false;
30 int midX = (topLeftX + lowRightX) / 2, midY = (topLeftY + lowRightY) / 2;
31 if (array[midX][midY] == target) return true;
32 else if (array[midX][midY] > target)
33 return find(topLeftX, topLeftY, midX - 1, lowRightY, target, array) ||
34 find(midX, topLeftY, lowRightX, midY - 1, target, array);
35
36 else
37 return find(topLeftX, midY + 1, midX, lowRightY, target, array) ||
38 find(midX + 1, topLeftY, lowRightX, lowRightY, target, array);
39
40 }
41 }
JZ11 旋转数组的最小数字
1 /* 双指针 */
2 public class JZ11_1
3 {
4 public static int minNumberInRotateArray(int[] nums)
5 {
6 if (nums[nums.length - 1] > nums[0]) return nums[0];
7 int i = 0, j = nums.length - 1;
8 while (nums[i] <= nums[i + 1] && nums[j] >= nums[j - 1])
9 {
10 i++;
11 j--;
12 }
13 return Math.min(nums[i + 1], nums[j]);
14 }
15 }
16
17 /* ⭐二分⭐ */
18 public class JZ11_2
19 {
20 public static int minNumberInRotateArray(int[] nums)
21 {
22 int left = 0, right = nums.length - 1, mid = -1;
23 while (left < right)
24 {
25 if (nums[left] < nums[right]) return nums[left];
26 mid = (left + right) / 2;
27 if (nums[mid] > nums[left]) left = mid + 1;
28 else if (nums[mid] < nums[right]) right = mid;
29 else left++;
30 }
31 return nums[left];
32 }
33 }
JZ38 字符串的排列
1 /* 递归1 */
2 public class JZ38_1
3 {
4 public static HashSet<String> SSet = new HashSet<>();
5 public static boolean[] vis;
6
7 public static ArrayList<String> Permutation(String str)
8 {
9 vis = new boolean[str.length()];
10 Permutation(str, new StringBuilder());
11 return new ArrayList<>(SSet);
12 }
13
14 public static void Permutation(String str, StringBuilder temp)
15 {
16 if (temp.length() == str.length())
17 {
18 SSet.add(temp.toString());
19 return;
20 }
21 for (int i = 0; i < str.length(); i++)
22 {
23 if (vis[i]) continue;
24 vis[i] = true;
25 temp.append(str.charAt(i));
26 Permutation(str, temp);
27 temp.deleteCharAt(temp.length() - 1);
28 vis[i] = false;
29 }
30 }
31 }
32
33 /* 递归2 */
34 public class JZ38_2
35 {
36 public static HashSet<String> res = new HashSet<String>();
37
38 public ArrayList<String> Permutation(String str)
39 {
40 Permutation(str.toCharArray(), 0);
41 return new ArrayList<>(res);
42 }
43
44 public void Permutation(char[] strArr, int begin)
45 {
46 if (begin == strArr.length - 1)
47 res.add(String.valueOf(strArr));
48 else
49 {
50 for (int i = begin; i < strArr.length; i++)
51 {
52 swap(strArr, begin, i);
53 Permutation(strArr, begin + 1);
54 swap(strArr, begin, i);
55 }
56 }
57 }
58
59 public void swap(char[] strArr, int a, int b)
60 {
61 char temp = strArr[a];
62 strArr[a] = strArr[b];
63 strArr[b] = temp;
64 }
65 }
JZ44 数字序列中某一位的数字
1 /* 模拟 */
2 public class JZ44_1
3 {
4 public static int findNthDigit(int n)
5 {
6 long t = 9, s, y, num, idx = 1, N = n;
7 if (N < 10) return (int) N;
8 while (N >= t * idx)
9 {
10 N = N - t * idx;
11 t *= 10;
12 idx++;
13 }
14 s = (N - 1) / idx;
15 y = (N - 1) % idx;
16 num = t / 9 + s;
17 return ("" + num).charAt((int) y) - '0';
18 }
19 }
