【leetCode刷题记录】-167. Two Sum II - Input array is sorted（双指针）

【2019/03/03】

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:

【思路】：

• 由于数组已经排好序了，利用升序的性质，用O（n）的时间复杂度完成；
• 用两个指针left和right分别指向数组的第一个和最后一个元素
• 当tmp = target的时候就返回两个值的索引值；
• 当tmp < target的时候，左值 ++；
• 当tmp > target的时候，右值 --；
• 返回的时候indices的值都要＋1（因为题目要求不能是zero-based）

【代码如下】

class Solution {
public:
    vector<int> twoSum(vector<int>& numbers, int target)
    {
    	vector<int> ret(2, -1);
    	int left = 0;
    	int right = numbers.zise - 1;
    	while( left < right )
    	{
    		int tmp = numbers[left] + numbers[right];
    		if( tmp == target)
    	    {
    	    	ret[0] = left + 1;
    	    	ret[1] = right + 1;
    	    	break;
    		}
    		else if (tmp < target)
    		{
    			left ++;
    		}
    		else
    			right--;
    	}
    	return ret;
    }
};