163. Missing Ranges

Description

Given a sorted integer array nums, where the range of elements are in the inclusive range****[lower, upper]**, return its missing ranges.

Example:

Input: nums = [0, 1, 3, 50, 75], lower = 0 and upper = 99,
Output: ["2", "4->49", "51->74", "76->99"]

Solution

题目看似不难，但是有坑，很容易会overflow。考虑下面这个test case:

[2147483647]
-2147483648
2147483647

还有这个：

[-2147483648,-2147483648,0,2147483647,2147483647]
-2147483648
2147483647

感觉不用long的话，很难避免overflow。
还需要注意的是，nums虽然是sorted，但可能有重复元素哦。

Iteration, time O(n), space O(1)

class Solution {
    public List findMissingRanges(int[] nums, int lower, int upper) {
        long need = lower;  // use long to avoid overflow
        List missingRanges = new ArrayList<>();
        
        for (int num : nums) {
            if (need < num) {
                missingRanges.add(getRange((int) need, num - 1));
            }
            
            need = 1l + num;    // don't overflow here!
        }
        
        if (need <= upper) {
            missingRanges.add(getRange((int) need, upper));
        }
        
        return missingRanges;
    }
    
    public String getRange(int n1, int n2) {
        return (n1 == n2) ? String.valueOf(n1) 
            : String.format("%d->%d", n1, n2);  // elegant
    }
}