34 Search for a Range
1. Question
Given an array of integers sorted in ascending order, find the starting and ending position of a given target value.
Your algorithm's runtime complexity must be in the order of O(logn).
If the target is not found in the array, return[-1, -1]
.
For example,
Given[5, 7, 7, 8, 8, 10]
and target value 8,
return[3, 4]
.
2. Implementation
(1) Binary Search
class Solution {
public int[] searchRange(int[] nums, int target) {
int[] res = {-1, -1};
if (nums == null || nums.length == 0) {
return res;
}
int start = 0, end = nums.length - 1, mid = 0;
while (start + 1 < end) {
mid = start + (end - start) / 2;
if (nums[mid] < target) {
start = mid + 1;
}
else {
end = mid;
}
}
if (nums[start] == target) {
res[0] = start;
}
else if (nums[end] == target) {
res[0] = end;
}
else {
return res;
}
end = nums.length - 1;
while (start + 1 < end) {
mid = start + (end - start) / 2;
if (nums[mid] > target) {
end = mid - 1;
}
else {
start = mid;
}
}
if (nums[end] == target) {
res[1] = end;
}
else if (nums[start] == target) {
res[1] = start;
}
else {
return res;
}
return res;
}
}
3. Time & Space Complexity
Binary Search: 时间复杂度O(logn), 空间复杂度O(1)
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