Compare Prefix and Postfix Increment and Decrement
Solve this ProblemEasy10 min
Topics
BasicsOperators
Companies
TCSInfosysWipro
Given an integer
x, run a = x++, b = ++x, c = x-- and d = --x in that order and return [a, b, c, d, x].
Increment and decrementIncrement / DecrementThe ++ and -- operators, which add or subtract 1 from a variable in place. operators change a variable by one, but where you put them matters. In prefixPrefix (++x)The variable is changed first and the expression gives the new value. form the change happens before the value is used; in postfixPostfix (x++)The expression gives the current value, and the variable is changed afterwards. form it happens after. Python has no ++ or --, so its solutions use the expanded form, which is also the clearest way to see what the operators do.
Test Case 1:
Input:x = 5
Output:[5,7,7,5,5]
Explanation:a = x++ keeps 5; b = ++x sees 7; c = x-- keeps 7; d = --x sees 5; x ends where it started.
Test Case 2:
Input:x = -3
Output:[-3,-1,-1,-3,-3]
Explanation:The same pattern works for negative numbers.
Constraints
- ◆
-1000 ≤ x ≤ 1000
Try the Dry Run
Approach & Solutions
Expanded AssignmentsGood
Write out what each operator does as two separate statements. Postfix (x++, x--): copy the current value first, then change x. Prefix (++x, --x): change x first, then copy the new value. Python has no ++ or --, so this expanded form is how Python always writes it.
Time
O(1)Space
O(1)Java
class Solution {
public int[] incrementTrace(int x) {
int a = x;
x = x + 1;
x = x + 1;
int b = x;
int c = x;
x = x - 1;
x = x - 1;
int d = x;
return new int[] {a, b, c, d, x};
}
}Prefix and Postfix OperatorsOptimal
Use the operators directly: a = x++, b = ++x, c = x--, d = --x. The position of ++ or -- decides whether the variable receives the value before or after the change. Python has no such operators, so its code stays the same as the expanded version.
Time
O(1)Space
O(1)Java
class Solution {
public int[] incrementTrace(int x) {
int a = x++;
int b = ++x;
int c = x--;
int d = --x;
return new int[] {a, b, c, d, x};
}
}