475. Heaters - Jing blog -

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 seperately, and your expected output will be the minimum radius standard of heaters.

Note:

Numbers of houses and heaters you are given are non-negative and will not exceed 25000.
Positions of houses and heaters you are given are non-negative and will not exceed 10^9.
As long as a house is in the heaters’ warm radius range, it can be warmed.
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.

思路：

这道题想了半天，用了几种方法都没解出来，后来看了提示醒悟了，主要问题在于每个house只要找最近的2个heater，取最大值。用house做遍历，heater作为辅助。虽然解出来了，但还是似懂非懂的。标记了

public class Solution {
    public int findRadius(int[] houses, int[] heaters) {
        Arrays.sort(houses);
        Arrays.sort(heaters);   
        int i = 0, j = 0, res = 0;
        while (i < houses.length) {
            while (j < heaters.length - 1 && Math.abs(heaters[j + 1] - houses[i]) <= Math.abs(heaters[j] - houses[i])) {
                j++;
            }
            res = Math.max(res, Math.abs(heaters[j] - houses[i]));
            i++;
        }
        return res;
    }
}

网上找到一个比较容易理解的方法：

public class Solution {  
    public int findRadius(int[] houses, int[] heaters) {  
        Arrays.sort(houses);  
        Arrays.sort(heaters);  
        int result = 0;  
        int temp = 0;  
        int j = 0;  
        for (int i = 0; i < houses.length; i++) {  
            while (j < heaters.length && heaters[j] < houses[i])  
                j++;  
            if (j == heaters.length)  
                temp = houses[i] - heaters[j - 1];  
            else if (j == 0)  
                temp = heaters[j] - houses[i];  
            else if (heaters[j] > houses[i])  
                temp = Math.min(heaters[j] - houses[i], houses[i] - heaters[j - 1]);  
            if (temp > result)  
                result = temp;  
        }  
        return result;  
    }  
}

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