Leetcode: Missing Number

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?

public class Solution {
public int missingNumber(int[] nums) {
int res = nums.length;
for (int i=0; i<nums.length; i++) {
if (nums[i] < nums.length && nums[nums[i]] != nums[i]) {
int temp = nums[nums[i]];
nums[nums[i]] = nums[i];
nums[i] = temp;
i--;
}
}
for (int i=0; i<nums.length; i++) {
if (nums[i] != i) res = i;
}
return res;
}
}