HDU 4961 boring sum (Thinking hash scan)

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Question: Here is an array for you to generate two new arrays. A requires that each number be located before it, and the nearest one is its multiple, then it becomes the number. Otherwise, it is your own. C is to find it later, and the sum of output cross-multiplication is

Analysis:

This is the complexity of O (N * SQRT (N). The limit data definitely times out, but the data in this question is a bit watery, so you can pass it.

Use the VIS [I] array to represent the position of the number nearest to the number I in the [], because all numbers are in the range of 1-, so it is feasible to scan it again, find the divisor of the current number, overwrite the divisor, and overwrite the/divisor.

The same is true if you look for a multiple number closest to this number and then multiply it.

 

1 # include <iostream> 2 # include <cstdio> 3 # include <cstring> 4 # include <cstdlib> 5 # include <cmath> 6 # include <algorithm> 7 # define LL _ int64 8 const int maxn = 100000 + 10; 9 Using namespace STD; 10 ll a [maxn], pre [maxn], AF [maxn], vis [maxn], sum; 11 12 INT main () 13 {14 int N, I, j, TMP; 15 while (~ Scanf ("% d", & N) 16 {17 memset (AF, 0, sizeof (AF); 18 memset (PRE, 0, sizeof (pre); 19 memset (VIS, 0, sizeof (VIS); 20 for (I = 1; I <= N; I ++) 21 scanf ("% i64d", & A [I]); 22 for (I = 1; I <= N; I ++) 23 {24 if (vis [A [I]) 25 pre [I] = A [vis [A [I]; 26 else27 pre [I] = A [I]; 28 TMP = (INT) SQRT (A [I]); 29 for (j = 1; j <= TMP; j ++) 30 if (a [I] % J = 0) 31 {32 vis [J] = I; 33 vis [A [I]/J] = I; // do not forget that SQRT is followed by the divisor 34} 35} 36 37 memset (VIS, 0, sizeof (VIS); 38 for (I = N; i> = 1; I --) 39 {40 if (vis [A [I]) 41 AF [I] = A [vis [A [I]; 42 else43 AF [I] = A [I]; 44 TMP = (INT) SQRT (A [I]); 45 for (j = 1; j <= TMP; j ++) 46 if (a [I] % J = 0) 47 {48 vis [J] = I; 49 vis [A [I]/J] = I; 50} 51} 52 sum = 0; 53 for (I = 1; I <= N; I ++) 54 sum + = pre [I] * AF [I]; 55 printf ("% i64d \ n", sum); 56} 57 Return 0; 58}

 

HDU 4961 boring sum (Thinking hash scan)