475. Heaters

Q:

Winter is coming! Your first job during the contest is to design a standard heater with fixed warm radius to warm all the houses.

Now, you are given positions of houses and heaters on a horizontal line, find out minimum radius of heaters so that all houses could be covered by those heaters.

So, your input will be the positions of houses and heaters separately, and your expected output will be the minimum radius standard of heaters.

Note:

1. Numbers of houses and heaters you are given are non-negative and will not exceed 25000.
2. Positions of houses and heaters you are given are non-negative and will not exceed 10^9.
3. As long as a house is in the heaters' warm radius range, it can be warmed.
4. All the heaters follow your radius standard and the warm radius will the same.

Example 1:

Input: [1,2,3],[2]
Output: 1
Explanation: The only heater was placed in the position 2, and if we use 

the radius 1 standard, then all the houses can be warmed.

Example 2:

Input: [1,2,3,4],[1,4]
Output: 1
Explanation: The two heater was placed in the position 1 and 4. 

We need to use radius 1 standard, then all the houses can be warmed.

A:

对于每个house，找到他应该最近的heater

public class Solution {
    public int findRadius(int[] houses, int[] heaters) {
        Arrays.sort(houses);
        Arrays.sort(heaters);
        int res= 0, i = 0 , n = heaters.length;
        for(int val : houses){// each house found its closest heater
            // if val is on left of i
            if(val <= heaters[i]){
                res = Math.max(res, heaters[i]  - val);
                continue;
            }
            // Now val > heaters[i]
            while(i+1<n && val > heaters[i+1])// move val in the middle of the closes heater
                i++;
            int rLeft = val - heaters[i];
            int rRight = i+1 < n ? heaters[i+1]-val : Integer.MAX_VALUE;
            res = Math.max(res, Math.min(rLeft, rRight));
        }
        return res;
    }
}

*******精简后的版本， 思路同上. ************ 

public class Solution {
    public int findRadius(int[] houses, int[] heaters) {
        Arrays.sort(houses);
        Arrays.sort(heaters);
        int res= 0, i = 0 ;
        for(int val : houses){// each house found its closest heater
            while(i+1<heaters.length && val > heaters[i+1])//move val in the middle of the closes heater
                i++;
            int rLeft = Math.abs(val - heaters[i]);
            int rRight = i+1 < heaters.length ? Math.abs(heaters[i+1]-val) : Integer.MAX_VALUE;
            res = Math.max(res, Math.min(rLeft, rRight));
        }
        return res;
    }
}

Errors:1：  没有考虑，可能一下子跳过很多heater ,house 直接跑到遥远的最后面  的情况。 （因此才要用while 来update index
2：  艹        原来默认的两个数组已经排序好， 是不成立的。  自己其实也一直在找，是不是已经排序好了。