```java
class Solution {
public int missingNumber(int[] nums) {
int left = 0;
int right = nums.length - 1;
while (left <= right) {
int mid = left + (right - left)/2;
if (nums[mid] < mid) {
left = mid + 1;
} else if (nums[mid] > mid) {
right = mid - 1;
} else if (nums[mid] == mid) {
left = mid + 1;
}
}
return left;
}
}
/*
[0,1,3]
1
mid + 1
*/
```ja
