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Copy pathMissingNumber.cpp
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54 lines (49 loc) · 1.78 KB
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// Source : https://leetcode.com/problems/missing-number/
// Author : Hao Chen
// Date : 2015-10-22
/***************************************************************************************
*
* 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?
*
* Credits:Special thanks to @jianchao.li.fighter for adding this problem and creating
* all test cases.
*
***************************************************************************************/
class Solution {
public:
// This problem can be converted to the classic problem --
// `There is an array, all of numbers except one appears twice, and that one only appears once`
// It means, we can combin two arrays together, one is [1..n], another one is `nums`.
// Then, you know, we can use the XOR solve this problem.
int missingNumber01(vector<int>& nums) {
int result = 0;
for(int i=0; i<nums.size(); i++){
result ^= nums[i];
}
for(int i=1; i<=nums.size(); i++){
result ^=(i);
}
return result;
}
// We can simplify the previous solution as below
int missingNumber02(vector<int>& nums) {
int result = 0;
for(int i=0; i<nums.size(); i++){
result = result ^ (i+1) ^ nums[i];
}
return result;
}
int missingNumber(vector<int>& nums) {
//By Leetcode running result, they all are same performance
return missingNumber02(nums); //36ms
return missingNumber01(nums); //36ms
}
};