贪心问题

1055. 股票买卖 II - AcWing题库

import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int[] a = new int[100010];
        int n = sc.nextInt();
        
        for(int i = 0; i < n; i ++){
            a[i] = sc.nextInt();
        }
        
        int res = 0;
        for(int i = 0; i < n - 1; i ++){
            res += Math.max(0, a[i + 1] - a[i]);
        }
        System.out.print(res);
    }
}

104. 货仓选址 - AcWing题库

import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[100010];
        for(int i = 0; i < n; i ++){
            a[i] = sc.nextInt();
        }
        
        Arrays.sort(a, 0, n);
        int res = 0;
        for(int i = 0; i < n; i ++){
            res += Math.abs(a[i] - a[n / 2]);
        }
        System.out.print(res);
    }
}

122. 糖果传递 - AcWing题库

本质上是一个货仓选址问题

import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] a = new long[1000010];
        long[] c = new long[1000010];
        
        long sum = 0;
        for(int i = 0; i < n; i ++){
            a[i] = sc.nextInt();
            sum += a[i];
        }
        
        long avg = sum / n;
        c[n - 1] = avg - a[n - 1];
        for(int i = n - 2; i > 0; i --){
            c[i] = c[i + 1] + avg - a[i]; 
        }
        Arrays.sort(c, 0, n);
        
        long res = 0;
        for(int i = 0; i < n; i ++){
            res += Math.abs(c[i] - c[n / 2]);
        }
        
        System.out.print(res);
    }
}

112. 雷达设备 - AcWing题库

1235. 付账问题 - AcWing题库

import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double S = sc.nextDouble();
        int[] a = new int[n];
        
        for(int i = 0; i < n; i ++){
            a[i] = sc.nextInt();
        }
        Arrays.sort(a, 0, n);
        
        double avg = S / n;
        double res = 0;
        for(int i = 0; i < n; i ++){
            double cur = S / (n - i);
            if(a[i] < cur) cur = a[i];
            res += (cur - avg) * (cur - avg);
            S -= cur;
        }
        
        System.out.printf("%.4f", Math.sqrt(res / n));
    }
}

1239. 乘积最大 - AcWing题库

import java.util.*;

public class Main{
    static int N = 100010;
    static long mod = 1000000009;
    static int[] a = new int[N];
    static int n, k;
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();
        k = sc.nextInt();
        for(int i = 0; i < n; i ++){
            a[i] = sc.nextInt();
        }
        Arrays.sort(a, 0, n);
        
        int l = 0, r = n - 1;
        long res = 1;
        int sign = 1;
        if(k % 2 == 1){
            res = a[r --];
            k --;
            if(res < 0) sign = -1; 
        }
        
        while(k > 0){
            long x = (long)a[l] * a[l + 1];
            long y = (long)a[r] * a[r - 1];
            if(x * sign > y * sign){
                res = x % mod * res % mod;
                l += 2;
            }else{
                res = y % mod * res % mod;
                r -= 2;
            }
            k -= 2;
        }
        
        System.out.print(res);
    }
}