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Problem 1 Two Sum

Language

JavaScript Java

Description

Given an array of integers, return indices of the two numbers such that they add up to a specific target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example

Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,return [0, 1].

Analysis

Set an array a=[] to save potential pairs, traverse the whole nums to try each number to find out that whether it equal to target-num[index], then we can figure out the indices.

Solution

JavaScript

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
    var a=[];
    for(let index=0,len=nums.length;index<len;index++){
        let temp=target-nums[index];
        if(a[temp]!==undefined)
            return [a[temp],index];
        a[nums[index]]=index;
    }
};

Java

class Solution {
    public int[] twoSum(int[] nums, int target) {
       for(int i=0;i<nums.length;i++){
           for(int j=i+1;j<nums.length;j++){
               if(nums[j]==target-nums[i]){
                   return new int[] {i,j};
               }
           }
       }
        throw new IllegalArgumentException("No two sum solution");
    }
}