Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.
If target is not found in the array, return [-1, -1].
You must write an algorithm with O(log n) runtime complexity.
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| Example 1:
Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]
Example 2:
Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]
Example 3:
Input: nums = [], target = 0
Output: [-1,-1]
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Constraints:
- 0 <= nums.length <= 10^5
- -10^9 <= nums[i] <= 10^9
- nums is a non-decreasing array.
- -10^9 <= target <= 10^9
Solution#
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| class Solution {
public int[] searchRange(int[] nums, int target) {
int lo = 0;
int hi = nums.length - 1;
while (lo <= hi) {
int mid = lo + (hi - lo) / 2;
if (nums[mid] == target) {
// 12345 6 6666666667890
if (mid == 0 || nums[mid - 1] != target) {
lo = mid;
break;
} else {
hi = mid - 1;
}
} else if (nums[mid] < target) {
lo = mid + 1;
} else {
hi = mid - 1;
}
}
if (nums.length == 0 || lo > hi || nums[lo] != target) {
return new int[] {-1, -1};
}
int[] res = new int[] {lo, -1};
lo = 0;
hi = nums.length - 1;
while (lo <= hi) {
int mid = lo + (hi - lo) / 2;
if (nums[mid] == target) {
// 12345666666666 6 7890
if (mid == nums.length - 1 || nums[mid + 1] != target) {
hi = mid;
break;
} else {
lo = mid + 1;
}
} else if (nums[mid] < target) {
lo = mid + 1;
} else {
hi = mid - 1;
}
}
res[1] = hi;
return res;
}
public int[] searchRangeLinear(int[] nums, int target) {
int lo = 0;
int hi = nums.length - 1;
while (lo < hi) {
int mid = lo + (hi - lo) / 2;
// 123456789
// ^
// 5
// lo hi
if (nums[mid] < target) {
lo = mid + 1;
} else {
hi = mid;
}
}
if (nums.length == 0 || nums[lo] != target) {
return new int[] {-1, -1};
}
int start = lo;
// linear scan
while (start + 1 < nums.length && nums[lo] == nums[start + 1]) {
start++;
}
return new int[] {lo, start};
}
}
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Solution 2021-11-29#
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| class Solution {
public int[] searchRange(int[] nums, int target) {
int lo = binarySearch(nums, target, true);
if (lo == -1 || nums[lo] != target) {
return new int[] {-1, -1};
}
int hi = binarySearch(nums, target, false);
return new int[] {lo, hi};
}
int binarySearch(int[] nums, int target, boolean isFirst) {
int lo = 0;
int hi = nums.length - 1;
while (lo <= hi) {
int mid = lo + (hi - lo) / 2;
if (nums[mid] == target) {
if (isFirst) {
if (mid == lo || target != nums[mid - 1]) {
return mid;
}
hi = mid - 1;
} else {
if (mid == hi || target != nums[mid + 1]) {
return mid;
}
lo = mid + 1;
}
} else if (nums[mid] > target) {
hi = mid - 1;
} else {
lo = mid + 1;
}
}
return -1;
}
}
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