剑指 Offer 53 - II. 0～n-1中缺失的数字

class Solution {
    public int missingNumber(int[] nums) {
        if(nums.length < 1) return 0;
        int l = 0;
        int r = nums.length - 1;
        while(l < r){
            int mid = l + r >> 1;
            if(nums[mid] != mid) r = mid;
            else l = mid + 1;
        }

        if( r == nums[r]) r ++;  //全部连续
        return r;

    }
}