leetcode-268

Missing Number

题目

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

For example,
Given nums = [0, 1, 3] return 2.

Note:

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

解题思路

a^b^b =a,

which means two xor operations with the same number will eliminate the number and reveal the original number.

普通方法（java-17ms）

public int missingNumber(int[] nums) {        Arrays.sort(nums);        int i;        for(i = 0;i<nums.length;i++){            if(nums[i] != i){                return i;            }        }        return i;    }

异或按位运算（java-1ms）

public int missingNumber(int[] nums) {    int xor = 0, i = 0;for (i = 0; i < nums.length; i++) {xor = xor ^ i ^ nums[i];}return xor ^ i;}

原题地址