Project Euler Problems in Go

problem1.go

package main

func Problem1() int {
  sum := 0
  for i := 0; i < 1000; i++ {
    if i % 3 == 0 || i % 5 == 0 {
      sum += i
    }
  }
  return sum
}

problem2.go

package main

const UPPER_BOUND = 4000000

func Problem2() int {
  // Initialize evenSum at 2 because oneBefore is included in result
  evenSum, localSum := 2, 0
  twoBefore, oneBefore := 1, 2

  for {
    localSum = oneBefore + twoBefore

    if (localSum > UPPER_BOUND) {
      break
    }

    if localSum % 2 == 0 {
      evenSum += localSum
    }

    // Shift previous variables
    twoBefore = oneBefore
    oneBefore = localSum
  }

  return evenSum
}

problem3.go

package main

func Problem3() int {
  i := 2
  n := 600851475143

  for i * i < n {
    for n % i == 0 {
      n = n / i
    }
    i += 1
  }

  return n
}

problem4.go

package main

func isPalindrome(num int) bool {
  reversed := 0
  n := num
  for n > 0 {
    reversed = reversed * 10 + n % 10
    n = n / 10
  }

  return reversed == num
}

func Problem4() int {
  a, b := 999, 999
  sum := 0
  flip := true

  for {
    sum = a * b

    if isPalindrome(sum) {
      return sum
    }

    // Iterate variables
    if flip {
      a -= 1
    } else {
      b -= 1
    }
    flip = !flip
  }
}

problem5.go

package main

func isDivisible(num int) bool {
  for i := 1; i < 21; i++ {
    if num % i != 0 {
      return false
    }
  }
  return true
}

func Problem5() int {
  n := 0
  for {
    n += 1
    if isDivisible(n) {
      return n
    }
  }
}