Two Sum II - Input array is sorted
Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number.
The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2.
Note:
Your returned answers (both index1 and index2) are not zero-based.
You may assume that each input would have
exactly
one solution and you may not use the
same
element twice.
Example:
Input: numbers = [2,7,11,15], target = 9
Output: [1,2]
Explanation: The sum of 2 and 7 is 9. Therefore index1 = 1, index2 = 2.
Solution
class Solution {
public int[] twoSum(int[] numbers, int target) {
// use binary search
int index1 = 0;
int index2 = 0;
for (int i = 0; i < numbers.length; i++) {
int val = numbers[i];
int found = Arrays.binarySearch(numbers, i + 1, numbers.length, target - val);
if (found >= 0) {
index1 = i + 1;
index2 = found + 1;
break;
}
}
return new int[]{ index1, index2 };
}
}
Solution using Two Pointers
class Solution {
public int[] twoSum(int[] numbers, int target) {
// use binary search
int start = 0;
int end = numbers.length - 1;
while (start < end) {
int sum = numbers[start] + numbers[end];
if (sum == target) {
return new int[]{ start + 1, end + 1 };
}
if (sum > target) {
end--;
} else {
start++;
}
}
return new int[]{ -1, -1 };
}
}
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