https://adventofcode.com/2020/day/1#part1

two_sum.go

package main

import "fmt"

func main() {
	nums := []int{
		1977,
		1802,
		1856,
		1309,
		2003,
		1854,
		1898,
		1862,
		1857,
		542,
		1616,
		1599,
		1628,
		1511,
		1848,
		1623,
		1959,
		1693,
		1444,
		1211,
		1551,
		1399,
		1855,
		1538,
		1869,
		1664,
		1719,
		1241,
		1875,
		1733,
		1547,
		1813,
		1531,
		1773,
		624,
		1336,
		1897,
		1179,
		1258,
		1205,
		1727,
		1364,
		1957,
		540,
		1970,
		1273,
		1621,
		1964,
		1723,
		1699,
		1847,
		1249,
		1254,
		1644,
		1449,
		1794,
		1797,
		1713,
		1534,
		1202,
		1951,
		1598,
		1926,
		1865,
		1294,
		1893,
		1641,
		1325,
		1432,
		1960,
		413,
		1517,
		1724,
		1715,
		1458,
		1775,
		1317,
		1694,
		1484,
		1840,
		1999,
		1811,
		1578,
		1658,
		1906,
		1481,
		1313,
		1997,
		1339,
		1592,
		1971,
		1453,
		1706,
		1884,
		1956,
		1384,
		1579,
		1689,
		1726,
		1217,
		1796,
		1536,
		1213,
		1867,
		1304,
		2010,
		1503,
		1665,
		1361,
		814,
		2007,
		1430,
		1625,
		1958,
		860,
		1799,
		1942,
		1876,
		1772,
		1198,
		1221,
		1814,
		1826,
		1667,
		1334,
		1504,
		1420,
		1164,
		1414,
		1934,
		1823,
		1507,
		1195,
		21,
		1752,
		1472,
		1196,
		1558,
		1322,
		1927,
		1556,
		1922,
		277,
		1828,
		1883,
		1280,
		1947,
		1231,
		1915,
		1235,
		1961,
		1494,
		1324,
		2009,
		1367,
		1545,
		1736,
		1575,
		1214,
		1704,
		1833,
		1663,
		1474,
		1894,
		1754,
		1564,
		1321,
		1119,
		1975,
		1987,
		1873,
		1834,
		1686,
		1574,
		1505,
		1656,
		1688,
		1896,
		1982,
		1554,
		1990,
		1902,
		1859,
		1293,
		1739,
		1282,
		1889,
		1981,
		1283,
		1687,
		1220,
		1443,
		1409,
		1252,
		1506,
		1742,
		1319,
		1882,
		951,
		1849,
	}

	m := make(map[int]int, len(nums))

	for _, num := range nums {
		if val, ok := m[num]; ok {
			fmt.Println(num * val)
			break
		}

		m[2020-num] = num
	}
}