【BZOJ3798】特殊的质数 分块打表

【BZOJ3798】特殊的质数

Description

求[A,B]之间的质数个数，并且满足X=Q^2+P^2,P,Q是正整数。

Input

第一行输入A，B

Output

输出有多少组P，Q满足条件

Sample Input

6 66

Sample Output

7

HINT

1<=A<=B<=3*10^8

题解：还有什么比表打错了更让人欲哭无泪的~

注意一下几点：

1.分块不能太小，10^5很稳，再小有可能装不下了

2.2=1*1+1*1，也算~

3.不要把x=i*i+0*0这样的算上

4.先开一个数组n2[i]=i*i比每次都计算i*i要快很多~（%popoqqq大爷的做法）

5.sqrt太慢了，用双指针法才能O(√n)判断x是不是两数平方的和

#include <cstdio>
#include <cstring>
#include <iostream>
#include <cmath>
using namespace std;
int ans;
int s[]={4784,8978,12981,16901,20732,24523,28249,31916,35585,39176,42818,46430,49962,53516,57023,60523,64040,67489,70985,74417,77879,81285,84679,88055,91433,94878,98240,101608,104979,108284,111653,115039,118375,121695,124997,128270,131626,134912,138219,141503,144830,148121,151368,154619,157925,161166,164444,167675,170946,174194,177433,180617,183844,187048,190283,193493,196709,199900,203111,206333,209526,212732,215966,219123,222272,225463,228651,231844,235069,238261,241443,244581,247733,250868,253974,257141,260352,263482,266623,269760,272885,276014,279149,282271,285396,288556,291710,294878,297984,301101,304177,307326,310444,313579,316642,319813,322904,326007,329106,332181,335268,338394,341465,344551,347665,350739,353840,356909,360000,363080,366160,369261,372328,375439,378518,381635,384728,387817,390920,393993,397033,400087,403209,406288,409309,412333,415431,418499,421556,424569,427583,430660,433680,436753,439791,442818,445857,448901,451962,454974,457972,461015,464069,467135,470153,473178,476215,479250,482265,485275,488279,491293,494311,497242,500236,503251,506276,509308,512383,515414,518404,521398,524428,527422,530472,533469,536442,539450,542467,545501,548499,551461,554513,557493,560489,563514,566514,569508,572481,575503,578464,581445,584484,587448,590416,593357,596373,599365,602379,605357,608340,611346,614316,617284,620283,623219,626204,629187,632137,635171,638124,641088,644018,646968,649933,652929,655897,658857,661819,664771,667743,670676,673688,676670,679672,682576,685541,688504,691478,694490,697405,700326,703273,706181,709115,712113,715038,717989,720960,723896,726882,729831,732782,735740,738676,741606,744563,747458,750384,753318,756217,759188,762199,765150,768087,771012,773928,776896,779827,782754,785698,788611,791513,794449,797361,800286,803241,806180,809116,812028,814963,817868,820796,823752,826720,829643,832596,835498,838436,841364,844292,847194,850080,853022,855895,858875,861761,864672,867592,870514,873482,876358,879282,882186,885138,888023,890933,893857,896758,899686,902573,905460,908421,911332,914214,917110,920007,922881,925822,928780,931678,934604,937520,940453,943326,946295,949181,952088,955026,957871,960726,963624,966507,969407,972309,975196,978085,980962,983867,986746,989647,992538,995405,998272,1001141,1004047,1006935,1009828,1012698,1015619,1018497,1021407,1024321,1027185,1030064,1032962,1035803,1038722,1041665,1044521,1047338,1050175,1053074,1055897,1058798,1061676,1064500,1067388,1070268,1073174,1076029,1078883,1081790,1084692,1087554,1090413,1093331,1096221,1099056,1101903,1104801,1107645,1110568,1113425,1116309,1119226,1122066,1124941,1127772,1130652,1133559,1136475,1139334,1142195,1145026,1147867,1150738,1153592,1156490,1159339,1162244,1165140,1168043,1170911,1173746,1176591,1179444,1182370,1185244,1188093,1190925,1193801,1196660,1199545,1202432,1205285,1208198,1211026,1213868,1216688,1219588,1222393,1225259,1228119,1230996,1233830,1236682,1239605,1242422,1245272,1248112,1250996,1253792,1256652,1259537,1262363,1265205,1268047,1270890,1273689,1276506,1279377,1282286,1285127,1287980,1290771,1293580,1296434,1299249,1302081,1304899,1307765,1310565,1313437,1316314,1319179,1321953,1324799,1327680,1330570,1333417,1336222,1339091,1341880,1344730,1347558,1350402,1353252,1356098,1358925,1361746,1364529,1367411,1370266,1373089,1375934,1378787,1381608,1384448,1387240,1390062,1392850,1395709,1398555,1401374,1404179,1407069,1409899,1412745,1415626,1418381,1421271,1424100,1426913,1429775,1432595,1435430,1438258,1441129,1443939,1446779,1449605,1452383,1455248,1458083,1460920,1463729,1466529,1469369,1472195,1475031,1477838,1480667,1483501,1486323,1489166,1491981,1494787,1497648,1500453,1503239,1506081,1508873,1511686,1514527,1517367,1520184,1523011,1525806,1528622,1531402,1534201,1536997,1539894,1542683,1545503,1548241,1551093,1553884,1556702,1559565,1562352,1565117,1567943,1570716,1573536,1576359,1579176,1581960,1584772,1587542,1590356,1593212,1596005,1598783,1601564,1604386,1607165,1609974,1612824,1615617,1618452,1621217,1624007,1626767,1629636,1632421,1635222,1637991,1640857,1643718,1646485,1649297,1652064,1654854,1657619,1660460,1663265,1666081,1668892,1671700,1674594,1677356,1680125,1682935,1685691,1688539,1691341,1694101,1696863,1699639,1702441,1705278,1708110,1710912,1713725,1716510,1719267,1722095,1724880,1727671,1730436,1733217,1736052,1738807,1741642,1744421,1747205,1750007,1752772,1755537,1758337,1761093,1763839,1766647,1769444,1772246,1775046,1777876,1780671,1783464,1786236,1789019,1791841,1794680,1797448,1800274,1803074,1805871,1808647,1811416,1814143,1816933,1819707,1822528,1825244,1828005,1830793,1833548,1836360,1839214,1841996,1844792,1847581,1850327,1853089,1855856,1858663,1861433,1864207,1866991,1869796,1872540,1875345,1878117,1880878,1883646,1886490,1889297,1892075,1894867,1897679,1900521,1903296,1906069,1908797,1911589,1914346,1917129,1919906,1922737,1925489,1928318,1931029,1933873,1936618,1939421,1942195,1944975,1947727,1950518,1953327,1956076,1958882,1961653,1964430,1967231,1969999,1972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int n2[20010];
bool sqr(int x)
{
	int i,j=(int)(sqrt(x)+1e-7)+1;
	for(i=1;n2[i]<x;i++)
	{
		for(;n2[i]+n2[j]>x;j--);
		if(n2[i]+n2[j]==x)	return true;
	}
	return false;
}
bool pri(int x)
{
	for(int i=2;n2[i]<=x;i++)	if(x%i==0)	return false;
	return true;
}
int calc(int n)
{
	if(n/100000)	ans=s[n/100000-1];
	else	ans=0;
	for(int i=n/100000*100000+1;i<=n;i++)
		if(pri(i)&&sqr(i))	ans++;
	return ans;
}
int main()
{
	int i,a,b;
	for(i=1;i<=20000;i++)	n2[i]=i*i;
	scanf("%d%d",&a,&b);
	printf("%d",calc(b)-calc(a-1));
	return 0;
}