2024/3/23 蓝桥杯

P1102 A-B 数对 二分

import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		//A-B=C
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int C = sc.nextInt();
		int[] res = new int[n+1];
		for(int i=1;i<=n;i++) {
			res[i] = sc.nextInt();
		}
		
		Arrays.sort(res,1,n+1);//1
		long ans = 0;//2
		
		for(int i=1;i<=n;i++) {//枚举B
			
			int l1 = i,r1 = n;//二分A
			while(l1<r1) {
				int mid = (l1+r1)/2;
				if(res[mid]-res[i]>=C)	r1 = mid;
				else	l1 = mid+1;
			}
			
			int l2 = i,r2 = n;
			while(l2<r2) {
				int mid = (l2+r2+1)/2;
				if(res[mid]-res[i]<=C)	l2 = mid;
				else	r2 = mid-1;
			}
			
			if(res[l2] - res[i] == C) {
				ans+=(l2-l1)+1;
			}
		}
		System.out.println(ans);
	}
}

789. 数的范围 二分

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int k = sc.nextInt();
		int[] res = new int[n];
		for(int i=0;i<n;i++)
			res[i] = sc.nextInt();
		while(k--!=0) {
			int x = sc.nextInt();
			//先大于等于再小于等于
			int l1 = 0,r1 = n-1;
			while(l1<r1) {
				int mid1 = (l1+r1)/2;
				if(res[mid1]>=x) r1 = mid1;
				else	l1 = mid1+1;
			}
			if(res[l1] == x) {
				int l2 = 0,r2 = n-1;
				while(l2<r2) {
					int mid2 = (l2+r2+1)/2;
					if(res[mid2]<=x) l2 = mid2;
					else	r2 = mid2-1; 
				}
				System.out.println(l1+" "+l2);
			}else {
				System.out.println("-1 -1");
			}
		}
	}
}