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34.Find-First-and-Last-Position-of-Element-in-Sorted-Array

34. Find First and Last Position of Element in Sorted Array

题目地址

题目描述

Given an array of integers nums 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(log n).
If the target is not found in the array, return [-1, -1].
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]

代码

class Solution {
public int[] searchRange(int[] nums, int target) {
int[] ans = {-1, -1};
int leftIndex = helper(nums, target, true);
if (leftIndex == nums.length || nums[leftIndex] != target) {
return ans;
}
ans[0] = leftIndex;
ans[1] = helper(nums,target, false);
return ans;
}
private int helper(int[] nums, int target, boolean isLeft) {
int low = 0;
int high = nums.length - 1;
while (low + 1 < high) {
int mid = low + (high - low) / 2;
if (nums[mid] == target) {
if (isLeft) {
high = mid;
} else {
low = mid;
}
}
else if (nums[mid] > target) {
high = mid;
}
else {
low = mid;
}
}
if (isLeft) {
if (nums[low] == target) {
return low;
} else if (nums[high] == target) {
return high;
}
} else {
if (nums[high] == target) {
return high;
} else if (nums[low] == target) {
return low;
}
}
return -1;
}
}

Approach #2

public class Solution {
public int[] searchRange(int[] A, int target) {
if (A.length == 0) return new int[]{-1, -1};
int start, end, mid;
int[] bound = new int[2];
start = 0;
end = A.length - 1;
while (start + 1 < end) {
mid = start + (end - start) / 2;
if (A[mid] == target) {
end = mid; // difference
} else if (A[mid] < target) {
start = mid;
} else {
end = mid;
}
}
if (A[start] == target) {
bound[0] = start;
} else if (A[end] == target) {
bound[0] = end;
} else {
bound[0] = bound[1] = -1;
return bound;
}
start = 0;
end = A.length - 1;
while (start + 1 < end) {
mid = start + (end - start) / 2;
if (A[mid] == target) {
start = mid; // difference
} else if (A[mid] < target) {
start = mid;
} else {
end = mid;
}
}
if (A[end] == target) {
bound[1] = end;
} else if (A[start] == target) {
bound[1] = start;
} else {
bound[0] = bound[1] = -1;
return bound;
}
return bound;
}
}