[prefix and notes] prefix and introduction and use

The prefix and ：（ Before similar series n Xiang He ）

use sum Before array record i Xiang He

sum[i]=a[0]+a[1]...+a[i]

purpose ： You can quickly find the interval 【i,j】 Sum of all numbers

  Subtract the two formulas to prove

    /* Prefixes and notes ：
     1.     It is known that num Array , Apply for another one of the same size sum Array
     2.   For the sake of calculation ,num Array and sum Arrays are all subscript 1 For the first element
     3.   Edge input , Edge update sum Array
           sum[0]=0;
           for(int i=1;i<=n;i++)
           {
            cin>>num[i];
            sum[i]=sum[i-1]+a[i];
           }
     4.   seek sum[i..j]( That is to say i The number to the first j The number and )
           sum[i..j]=sum[j]-sum[i-1]
             If i be equal to 1,sum[1..j]=sum[j]-sum[0]=sum[j]
             therefore ,num&&sum Array from 1 Start and sum[0]=0