475. Heaters

http://www.cnblogs.com/EdwardLiu/p/6197086.html

https://leetcode.com/problems/heaters/#/description

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.

Binary Search My solution:

Be careful in my binary search function, l, r may go out of the range of the array

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

}
return res;
}

二分查找法:

public class Solution {
public int findRadius(int[] houses, int[] heaters) {
Arrays.sort(heaters);
int result = Integer.MIN_VALUE;

for (int house : houses) {
int index = Arrays.binarySearch(heaters, house); // if put each house in heaters array, this is each house's insertion position
if (index < 0) {
index = -(index + 1);
}
int dist1 = index - 1 >= 0 ? house - heaters[index - 1] : Integer.MAX_VALUE; //this house's distance with heaters infront of it, maybe none in front
int dist2 = index < heaters.length ? heaters[index] - house : Integer.MAX_VALUE; //this house's distance with heaters after it

result = Math.max(result, Math.min(dist1, dist2));
}

return result;
}
}

public class Solution {
    public int findRadius(int[] houses, int[] heaters) {
        Arrays.sort(heaters);
        int minRange = Integer.MIN_VALUE;
        for (int house : houses) {
            int range = binarySearch(house, heaters);
            minRange = Math.max(minRange, range);
        }
        return minRange;
    }
    
    public int binarySearch(int house, int[] heaters) {
        int l=0, r=heaters.length-1;
        while (l <= r) {
            int m = (r-l)/2 + l;
            if (heaters[m] == house) return 0;
            else if (heaters[m] < house) l = m + 1;
            else r = m - 1;
        }
        if (l >= heaters.length) return Math.abs(heaters[r]-house);
        else if (r < 0) return Math.abs(heaters[l]-house);
        return Math.abs(heaters[r]-house)<Math.abs(heaters[l]-house)? Math.abs(heaters[r]-house) : Math.abs(heaters[l]-house);
    }
}