leetcode 34. Search for a Range

Given a sorted array of n integers, find the starting and ending position of a given target value.

If the target is not found in the array, return 

[-1, -1]

.
Example

Given 

[5, 7, 7, 8, 8, 10]

 and
target value 

8

,

return 

[3, 4]

.

分析：

这道题我们只需要分别对起点和终点用二分法就可以啦～

public class Solution {
/**
*@param A : an integer sorted array
*@param target :  an integer to be inserted
*return : a list of length 2, [index1, index2]
*/
public int[] searchRange(int[] A, int target) {
if (A.length == 0) {
return new int[]{-1, -1};
}
int[] result = new int[2];
int start, end;

//search the first element
start = 0;
end = A.length - 1;
while (start + 1 < end) {
int mid = start + (end - start) / 2;
if (A[mid] == target) {
end = mid;
} else if (A[mid] < target) {
start = mid;
} else {
end = mid;
}
}

if(A[start] == target) {
result[0] = start;
} else if (A[end] == target){
result[0] = end;
} else {
result[0] = result[1] = -1;
return result;
}

//search the second element
start = 0;
end = A.length - 1;
while (start + 1 < end) {
int mid = start + (end - start) / 2;
if (A[mid] == target) {
start = mid;
} else if (A[mid] < target) {
start = mid;
} else {
end = mid;
}
}

if(A[end] == target) {
result[1] = end;
} else if (A[start] == target){
result[1] = start;
} else {
result[0] = result[1] = -1;
return result;
}
return result;
}
}