Today #Day148 of #365DaysOfCode, I am Solving Leet code 1. Two Sum.
Question
Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.
You can return the answer in any order.
Example 1:
Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
Example 2:
Input: nums = [3,2,4], target = 6
Output: [1,2]
Example 3:
Input: nums = [3,3], target = 6
Output: [0,1]
Constraints:
2 <= nums.length <= 10<sup>4</sup>-10<sup>9</sup> <= nums[i] <= 10<sup>9</sup>-10<sup>9</sup> <= target <= 10<sup>9</sup>Only one valid answer exists.
Answer Leetcode:
var twoSum = (nums, target) => {
for (let curr = 0; curr < nums.length; curr++) {/* Time O(N) */
const complement = target - nums[curr];
for (let next = (curr + 1); next < nums.length; next++) {/* Time O(N) */
const num = nums[next];
const isTarget = num === complement
if (isTarget) return [ curr, next ];
}
}
return [ -1, -1 ];
}
Explanation,
for (let curr = 0; curr < nums.length; curr++) {/* Time O(N) */
This line initializes a variable curr to 0 and iterates through the array nums until curr is less than the length of the array. The time complexity of this loop is O(N), where N is the length of the input array.
const complement = target - nums[curr];
This line calculates the complement of the current element by subtracting it from the target number.
for (let next = (curr + 1); next < nums.length; next++) {/* Time O(N) */
This line initializes a variable next to the next index of the current element and iterates through the remaining elements of the array. The time complexity of this loop is O(N), where N is the length of the input array.
const num = nums[next];
This line assigns the value of the next element to a variable num.
const isTarget = num === complement;
This line checks if the current element and the complement add up to the target number.
if (isTarget) return [ curr, next ];
This line returns an array of two indices if the current element and the complement add up to the target number.
}
}
return [ -1, -1 ];
This line returns an array of two -1s if no two elements add up to the target number.
I hope this helps! Let me know if you have any other questions.
Conclusion
I solved the Leet code 1. Two Sum.