整数二分浮点二分代码模板

Posted 2022-02-06 知道什么是码怪吗？

二分不一定需要有序性，只需要确保二分的两边不同时满足某一性质即可。

目录

整数二分

练习题目：二分查找

练习题目：数的范围

浮点二分

练习题目：数的三次方根

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整数二分

整数二分会出现很多边界问题。

练习题目：二分查找

java题解

class Solution 
    public int search(int[] nums, int target) 
		// 二分查找
		int right = nums.length - 1;
		int left = 0;

		while (left <= right) 
			int mid = left + (right - left) / 2;
			if (target < nums[mid])
				right = mid - 1;// 注意right=mid-1
			else if (target > nums[mid])
				left = mid + 1;// 注意left=mid+1,而不是left=mid,不然会无限循环
			else if (target == nums[mid]) 
				return mid;
			
		
		return -1;
	

练习题目：数的范围

java题解

import java.util.Scanner;

public abstract class Main 

	public static void check(int[] nums, int number) 

		int left = 0;
		int right = nums.length - 1;

		while (left < right) // 查找这个数最右边出现的下标
			int mid = (left + right) / 2;
			if (nums[mid] >= number)
				right = mid;
			else
				left = mid + 1;
		

		if (nums[left] != number) // 没有找到这个数
			System.out.println("-1 -1");
			return;
		

		System.out.print(left + " ");

		left = 0;// 初始化
		right = nums.length - 1;
		while (left < right) // 查找这个数最左边出现的下标
			int mid = (left + right + 1) / 2;
			if (nums[mid] <= number)
				left = mid;
			else
				right = mid - 1;
		

		System.out.println(right);
	

	public static void main(String[] args) 

		Scanner input = new Scanner(System.in);
		int n = input.nextInt();
		int m = input.nextInt();
		int[] nums = new int[n];

		for (int i = 0; i < n; i++) // 接收数组
			nums[i] = input.nextInt();
		

		for (int i = 0; i < m; i++) 
			int temp = input.nextInt();
			check(nums, temp);// 输出结果
		
	

浮点二分

浮点二分不用考虑边界问题

练习题目：数的三次方根

java题解

import java.util.Scanner;

public abstract class Main 

	public static void main(String[] args) 

		Scanner input = new Scanner(System.in);
		double n = input.nextDouble();
		double left = -50, right = 50;
		
		while (right - left > 1e-8) //不用考虑边界问题，但是有浮点数有精度问题，精度应当高于要求保留的小数位
			double mid = (left + right) / 2;
			if (mid * mid * mid >= n)
				right = mid;
			else
				left = mid;
		
		System.out.printf("%.6f", left);