Palindrome Algorithms Ideas

checkIdeas.groovy

n = "99"
s = n.length()
println s%2==0 ? "${n[0..(s/2-1)]} ${n[s/2..-1]}" : "${n[0..(s/2-1)]} ${n[s.intdiv(2)]} ${n[s/2+1..-1]}"
println s%2==0 ? "${n[0..(s/2-1)] == n[s/2..-1]}" : "${n[0..(s/2-1)] == n[s/2+1..-1]}"
println s%2==0 ? n[0..(s/2-1)] == n[s/2..-1] : n[0..(s/2-1)] == n[s/2+1..-1]

palindromesBrutalForce.groovy

def isPl(n){s=n.length(); return  s%2==0 ? n[0..(s/2-1)] == n[-1..s/2] : n[0..(s/2-1)] == n[-1..s/2+1]   }
a=99
pl = [:]
acc = []
while(a>=10){
    for(b=99 ; b>=10; b--){
        acc << [a, b, a*b, isPl( (a*b).toString() )]
        if(isPl( (a*b).toString() )) pl << [(a*b):[a,b]]
    }
    a--
}

println pl.sort{ it.key }

palindromesDecrementadosDezPorDez.groovy

def isPl(n){s=n.length(); return  s%2==0 ? n[0..(s/2-1)] == n[-1..s/2] : n[0..(s/2-1)] == n[-1..s/2+1]   }
a = b = 999
def calc(a,b){
    if(a<=9 || b<=9 || isPl((a*b).toString())){
        return [a, b, a*b]
    }
    println "a: $a and b: $b | a*b = ${a*b} isPl(${ (a*b).toString() } == ${isPl((a*b).toString())})"
    
    if(a%10!=0){
        calc(--a, b)
        
    }else if(b%10!=0){
        calc(a, --b)
        
    }else{
        a>=b ? calc(--a, b) : calc(a, --b)
    }
}

calc(a,b)

palindromesDecrementadosUmPorUm.groovy

a = b = 100

def isPl(n){s=n.length(); return  s%2==0 ? n[0..(s/2-1)] == n[s/2..-1] : n[0..(s/2-1)] == n[s/2+1..-1]   }

def calc(a,b){
    if(a<=9 || b<=9){
        return false
    }
    println "a: $a and b: $b = ${ a*b } is palindrome (${ isPl((a*b).toString()) } )"
    b>=a ? calc(a, --b) : calc(--a, b)
}

calc(a,b)


//----


def isPl(n){s=n.length(); return  s%2==0 ? n[0..(s/2-1)] == n[-1..s/2] : n[0..(s/2-1)] == n[-1..s/2+1]   }
a=999
pl = [:]
acc = []
notFound = true
while(a>=100 && notFound){
    for(b=999 ; b>=100; b--){
        acc << [a, b, a*b, isPl( (a*b).toString() )]
        if(isPl( (a*b).toString() )) {pl << [(a*b):[a,b]]}
    }
    a--
}

println pl.sort{ it.key }