268. Missing Number

题目地址：https://leetcode.com/problems/missing-number/description/

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.

Example 1:

Input: [3,0,1]
Output: 2

Example 2:

Input: [9,6,4,2,3,5,7,0,1]
Output: 8

Note:
Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?

class Solution {
    public int missingNumber(int[] nums) {
        int sum = (nums.length + 1) * nums.length >>> 1; // 原本应该nums.length+1个数字，从0到nums.length，求和就行
        int sum1 = 0;
        for (int i = 0; i < nums.length; ++i) {
            sum1 += nums[i];
        }
        return sum - sum1;
    }
}

（CSDN的java模版是无法打出null的，不信你们去试试，反映给技术部无果，估计他们也解决不了）

Debug code in playground: 

class Solution {
    public int missingNumber(int[] nums) {
        int sum = (nums.length + 1) * nums.length >>> 1;
        int sum1 = 0;
        for (int i = 0; i < nums.length; ++i) {
            sum1 += nums[i];
        }
        return sum - sum1;
    }
}

public class MainClass {
    public static int[] stringToIntegerArray(String input) {
        input = input.trim();
        input = input.substring(1, input.length() - 1);
        if (input.length() == 0) {
          return new int[0];
        }
    
        String[] parts = input.split(",");
        int[] output = new int[parts.length];
        for(int index = 0; index < parts.length; index++) {
            String part = parts[index].trim();
            output[index] = Integer.parseInt(part);
        }
        return output;
    }
    
    public static void main(String[] args) throws IOException {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        String line;
        while ((line = in.readLine()) != null) {
            int[] nums = stringToIntegerArray(line);
            
            int ret = new Solution().missingNumber(nums);
            
            String out = String.valueOf(ret);
            
            System.out.print(out);
        }
    }
}

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