Sword finger offer 53 - ii Missing numbers from 0 to n-1

Title Description

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Problem analysis

Use the formula of arithmetic sequence to find n Xiang He , Then find the sum of the array , Subtract the two

Code instance

class Solution {
    
    public int missingNumber(int[] nums) {
    
        int n = nums.length;
        int a = n * (n + 1) / 2;
        int sum = 0;
        for(int i = 0;i < nums.length;i++){
    
            sum += nums[i];
        }
        return (a - sum);
    }
}