#148 Easy Time O(n) Space O(1) Animated

Missing Number

Find the missing number in range [0, n].

Tutor Mode Build the mental model before you memorize the code.

Pattern Bitwise state reduction

Use a bit operation to retain only the information the problem needs while discarding the rest.

Approach: Bitwise XOR / Math

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Core Insight

Use a bit operation to retain only the information the problem needs while discarding the rest.

Common Pitfall

Parenthesize shifts and masks, especially when mixing comparison or arithmetic operators.

Description

Find the missing number in range [0, n].

TimeO(n) SpaceO(1)

Implementation Plan

Translate the invariant into these small, testable moves.

def missingNumber(nums):
    res = len(nums)
    
    for i in range(len(nums)):
        res += (i - nums[i])
        
    return res