计蒜客 思维 奶酪工厂

思路：维护局部最优解。从这一次产品和上一次产品选择。

package BlueBrigdeReview;
  
  //import java.util.Scanner;
  import java.util.*;
  public class Main {
    public static void main(String[] args) {
      Scanner cin = new Scanner(System.in);
      int n = cin.nextInt();
      int s = cin.nextInt();
      long a[] = new long[n + 5];
      long b[] = new long[n + 5];
      
      for(int i = 0;i < n;i++) {
        a[i] = cin.nextLong();
        b[i] = cin.nextLong();
      }
      long min = (long)1e18, sum = 0;
//      long x = 0;
      for(int i = 0;i < n;i++) {
        min = Math.min(min + s, a[i]);
        sum += min * b[i];
      }
      System.out.println(sum);
    }
  }