• java cheatsheet methods https://tusharghosh09006.medium.com/cheat-sheet-on-java-collection-709ca96edc9d

pattern

• pascal triangle make with BIONOMIAL COEEFICIENT
  • c = c * (i-j) / j where i = [1, N] and j = [1, N]
    formula saying start from 1th index ( not 0 ) for(i=1 → n) c = 1 for( j=1 → i ) store c and then update c = c * (i-j) / j next = curr * (remaining) / choosen

basic math

• https://algo.monster/problems/math-basics

• reverse number

  • ans=0 while(digit != 0 ) mod = x%10; digit = digit/10; ans = ans*10+mod before setting up ans edge condition if ((ans > (INT_MAX - abs(digit))/10) || (ans < (INT_MIN + abs(digit))/10) ) return 0

• Armstrong number → 23 = 2³ + 3³ = 35

• HCF = GCD = biggest number that divides both

  • for i =0 → min(a, b) if ( a%i==0 and b%i ==0 ) then update ans
  • LCM(a,b) × GCD(a,b) = a×b
  • Euclidean Algorithm GCD(a, b) = GCD(b, a % b) GCD(48, 18) → 48 % 18 = 12 so gcd(18, 12) → 18 % 12 = 6 so gcd(12, 6) → 12 % 6 = 0 so gcd(6, 0) When b=0 → GCD = a always

Array

• sort color 0s-1s-2s
  • brute → merge sort TC nlogN SC n
  • better → count0 | count1 | count2 TC 2N
  • best → dutch national algo ( three pointer app. )
    • s,p =0 | e = lastInd while ( p<=e) p=0 —> swap(s,p) s++ p++ p=1 —> p++ p=2 —> swap(p,e) e - -
• move all neg nums on left side ( twoPointer )
  • s= 0 | e = lastInd if( s = -ve ) s++ else if ( e = +ve ) e - - else swap (s,e)
• find duplicate num
  • sort and then i, i+1
  • neg Marking
  • postion Method
• missing Ele from array with duplicate
  • sort then matching with 1indexing
  • neg marking
• Find first repeating ele
  • brute → n2
  • Hashmap
• common ele in 3 sorted array
  • i , j, k method
• spiral print matrix
  • rows = arr.size() , cols = arr[0].size() , startingRow, startingCol, endingRow, endingCol
  • ele < totalEle n*m