初级--03---二分复杂度哈希表和有序表
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文章目录
二分法
题目1
// arr保证有序
public static boolean find(int[] arr, int num) {
if (arr == null || arr.length == 0) {
return false;
}
int L = 0;
int R = arr.length - 1;
while (L <= R) {
int mid = (L + R) / 2;
if (arr[mid] == num) {
return true;
} else if (arr[mid] < num) {
L = mid + 1;
} else {
R = mid - 1;
}
}
return false;
}
测试-----制造对数器
package main.java.newcode;
import java.util.Arrays;
public class Code01_BSExist {
// arr保证有序
public static boolean find(int[] arr, int num) {
if (arr == null || arr.length == 0) {
return false;
}
int L = 0;
int R = arr.length - 1;
while (L <= R) {
int mid = (L + R) / 2;
if (arr[mid] == num) {
return true;
} else if (arr[mid] < num) {
L = mid + 1;
} else {
R = mid - 1;
}
}
return false;
}
// for test
public static boolean test(int[] sortedArr, int num) {
for (int cur : sortedArr) {
if (cur == num) {
return true;
}
}
return false;
}
// for test
public static int[] generateRandomArray(int maxSize, int maxValue) {
int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
for (int i = 0; i < arr.length; i++) {
arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
}
return arr;
}
public static void main(String[] args) {
int testTime = 500000;
int maxSize = 10;
int maxValue = 100;
boolean succeed = true;
for (int i = 0; i < testTime; i++) {
int[] arr = generateRandomArray(maxSize, maxValue);
Arrays.sort(arr);
int value = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
if (test(arr, value) != find(arr, value)) {
System.out.println("出错了！");
succeed = false;
break;
}
}
System.out.println(succeed ? "Nice!" : "Fucking fucked!");
}
}
题目2
// arr有序的，>=num 最左
public static int mostLeftNoLessNumIndex(int[] arr, int num) {
if (arr == null || arr.length == 0) {
return -1;
}
int L = 0;
int R = arr.length - 1;
int ans = -1;
while (L <= R) {
int mid = (L + R) / 2;
if (arr[mid] >= num) {
ans = mid;
R = mid - 1;
} else {
L = mid + 1;
}
}
return ans;
}
// 在arr上，找满足<=value的最右位置
public static int nearestIndex(int[] arr, int value) {
int L = 0;
int R = arr.length - 1;
int index = -1; // 记录最右的对号
while (L <= R) {
int mid = L + ((R - L) >> 1);
if (arr[mid] <= value) {
index = mid;
L = mid + 1;
} else {
R = mid - 1;
}
}
return index;
}
局部最小值问题
public class Code04_BSAwesome {
// arr 整体无序
// arr 相邻的数不相等！
public static int oneMinIndex(int[] arr) {
if (arr == null || arr.length == 0) {
return -1;
}
int N = arr.length;
if (N == 1) {
return 0;
}
if (arr[0] < arr[1]) {
return 0;
}
if (arr[N - 1] < arr[N - 2]) {
return N - 1;
}
int L = 0;
int R = N - 1;
// L...R 肯定有局部最小
while (L < R - 1) {
int mid = (L + R) / 2;
if (arr[mid] < arr[mid - 1] && arr[mid] < arr[mid + 1]) {
return mid;
} else {
if (arr[mid] > arr[mid - 1]) {
R = mid - 1;
} else {
L = mid + 1;
}
}
}
return arr[L] < arr[R] ? L : R;
}
// 生成随机数组，且相邻数不相等
public static int[] randomArray(int maxLen, int maxValue) {
int len = (int) (Math.random() * maxLen);
int[] arr = new int[len];
if (len > 0) {
arr[0] = (int) (Math.random() * maxValue);
for (int i = 1; i < len; i++) {
do {
arr[i] = (int) (Math.random() * maxValue);
} while (arr[i] == arr[i - 1]);
}
}
return arr;
}
// 也用于测试
public static boolean check(int[] arr, int minIndex) {
if (arr.length == 0) {
return minIndex == -1;
}
int left = minIndex - 1;
int right = minIndex + 1;
boolean leftBigger = left >= 0 ? arr[left] > arr[minIndex] : true;
boolean rightBigger = right < arr.length ? arr[right] > arr[minIndex] : true;
return leftBigger && rightBigger;
}
public static void printArray(int[] arr) {
for (int num : arr) {
System.out.print(num + " ");
}
System.out.println();
}
public static void main(String[] args) {
int maxLen = 100;
int maxValue = 200;
int testTime = 1000000;
System.out.println("测试开始");
for (int i = 0; i < testTime; i++) {
int[] arr = randomArray(maxLen, maxValue);
int ans = oneMinIndex(arr);
if (!check(arr, ans)) {
printArray(arr);
System.out.println(ans);
break;
}
}
System.out.println("测试结束");
}
}
时间复杂度
基础–04----时间、空间复杂度
哈希表
哈希表可以看成一个(K V)表
哈希表的增删改查,时间复杂度都可以看成 O(1)
哈希表分类:
- 引用传递
- 按值传递
HashMap
基础类型 : int double char string ------按值传递
public static void main(String[] args) {
HashMap<Integer, String> map2 = new HashMap<>();
map2.put(1234567, "我是1234567");
Integer a = 1234567;
Integer b = 1234567;
System.out.println(a == b);
System.out.println(map2.containsKey(a));
System.out.println(map2.containsKey(b));
}
对象类型 : int double char string ------引用传递
import java.util.HashMap;
import java.util.TreeMap;
public class Code05_HashMapTreeMap {
public static class Node {
public int value;
public Node(int v) {
value = v;
}
}
// (K V)表
public static void main(String[] args) {
Node node1 = new Node(1);
Node node2 = new Node(1);
HashMap<Node, String> map3 = new HashMap<>();
map3.put(node1, "我进来了！");
System.out.println(map3.containsKey(node1));
System.out.println(map3.containsKey(node2));
}
}
有序表
TreeMap的增删改查,时间复杂度都可以看成 O(n)
java数据结构
TreeMap
public static void main(String[] args) {
TreeMap<Integer, String> treeMap1 = new TreeMap<>();
treeMap1.put(3, "我是3");
treeMap1.put(0, "我是3");
treeMap1.put(7, "我是3");
treeMap1.put(2, "我是3");
treeMap1.put(5, "我是3");
treeMap1.put(9, "我是3");
System.out.println(treeMap1.containsKey(7));
System.out.println(treeMap1.containsKey(6));
System.out.println(treeMap1.get(3));
treeMap1.put(3, "他是3");
System.out.println(treeMap1.get(3));
treeMap1.remove(3);
System.out.println(treeMap1.get(3));
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