001-Two Sum

Posted 2020-09-18 airycode

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].

 

 

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package TWO_SUM_001;

import java.util.Arrays;


public class Main {

    public static void main(String[] args) {

        int nums[] = {2,7,11,15};
        int num[] = twoSum(nums,9);
        print(num);
        
    }

    private static void print(int[] num) {
        if (num != null && num.length>0) {
            for (int n:num) {
                System.out.print(n+" ");
            }
        }
        
    }

    public static int[] twoSum(int[] nums, int target) {
        int[] array = new int[2];
        //1:首先对数组中数字排序
        Arrays.sort(nums);
        //2:
        int start = 0;//下标
        int end = nums.length-1;//下标
        
        //从两边向中间靠拢
        while (start < end) {
            //找到输入的结果直接返回
            if (nums[start]+nums[end] == target) {
                
                if (nums[start] > nums[end]) {
                    array[0] = end+1;
                    array[1] = start+1;
                } else {
                    array[0] = start+1;
                    array[1] = end+1;
                }
                break;
            } else if (nums[start]+nums[end] > target) {//如果大于右边的值end--
                end--;
            } else {
                start++;
            }
        }
        return array;
    }

}