Leetcode - Missing Ranges

My code:

public class Solution {
    public List<String> findMissingRanges(int[] nums, int lower, int upper) {
        List<String> ret = new ArrayList<String>();
        if (nums == null) {
            return ret;
        }
        else if (nums.length == 0) {
            if (upper == lower) {
                ret.add("" + lower);
                return ret;
            }
            else {
                ret.add(lower + "->" + upper);
                return ret;
            }
        }
        
        int pre = lower;
        for (int i = 0; i < nums.length; i++) {
            if (i == 0) {
                if (nums[i] == pre + 1) {
                    ret.add("" + pre);
                }
                else if (nums[i] > pre + 1) {
                    ret.add(pre + "->" + (nums[i] - 1));
                }
                pre = nums[i];
            }
            else {
                if (nums[i] == pre + 2) {
                    ret.add("" + (pre + 1));
                }
                else if (nums[i] > pre + 2) {
                    ret.add((pre + 1) + "->" + (nums[i] - 1));
                }
                pre = nums[i];
            }
        }
        
        if (upper == pre + 1) {
            ret.add("" + upper);
        }
        else if (upper > pre + 1) {
            ret.add((pre + 1) + "->" + upper);
        }
        
        return ret;
    }
}

个人感觉这道题目没什么意思。。

Anyway, Good luck, Richardo! -- 09/04/2016

My code:

import java.util.ArrayList;
import java.util.List;

public class Solution {
    public List<String> findMissingRanges(int[] nums, int lower, int upper) {
        List<String> ret = new ArrayList<String>();
        long prev = (long) lower - 1;
        for (int i = 0; i <= nums.length; i++) {
            long curr = (i == nums.length ? upper + 1 : nums[i]);
            if (curr - prev >= 2) {
                ret.add(getRange(prev + 1, curr - 1));
            }
            prev = curr;
        }
        
        return ret;
    }
    
    private String getRange(long i, long j) {
        if (i == j) {
            return "" + i;
        }
        else {
            return i + "->" + j;
        }
    }
}

reference:
https://tonycao.gitbooks.io/leetcode-locked/content/LeetCode%20Locked/c1.8.html

这种解法更简洁高效。

Anyway, Good luck, Richardo! -- 10/16/2016