main3.cpp

/// Source : https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/description/
/// Author : liuyubobobo
/// Time   : 2017-11-13

#include <iostream>
#include <vector>
#include <cassert>

using namespace std;

// Two Pointers
// Time Complexity: O(n)
// Space Complexity: O(1)
class Solution {

public:
    vector<int> twoSum(vector<int>& numbers, int target) {

        assert(numbers.size() >= 2);
        // assert(isSorted(numbers));

        int l = 0, r = numbers.size() - 1;
        while(l < r){

            if(numbers[l] + numbers[r] == target){
                int res[2] = {l+1, r+1};
                return vector<int>(res, res+2);
            }
            else if(numbers[l] + numbers[r] < target)
                l ++;
            else // numbers[l] + numbers[r] > target
                r --;
        }

        throw invalid_argument("the input has no solution");
    }

private:
    bool isSorted(const vector<int>& numbers){
        for(int i = 1 ; i < numbers.size() ; i ++)
            if(numbers[i] < numbers[i-1])
                return false;
        return true;
    }

};

void printVec(const vector<int>& vec){
    for(int e: vec)
        cout << e << " ";
    cout << endl;
}

int main() {

    int nums[] = {2, 7, 11, 15};
    vector<int> vec(nums, nums + sizeof(nums) / sizeof(int));
    int target = 9;
    printVec(Solution().twoSum(vec, target));

    return 0;
}