1237. Find Positive Integer Solution for a Given Equation.cpp

/*
 * // This is the custom function interface.
 * // You should not implement it, or speculate about its implementation
 * class CustomFunction {
 * public:
 *     // Returns f(x, y) for any given positive integers x and y.
 *     // Note that f(x, y) is increasing with respect to both x and y.
 *     // i.e. f(x, y) < f(x + 1, y), f(x, y) < f(x, y + 1)
 *     int f(int x, int y);
 * };
 */

class Solution {
public:
    vector<vector<int>> findSolution(CustomFunction& customfunction, int z) {
        vector<vector<int>> res;
        for(int x=1;x<1000;x++)
        {
            int lo=1;
            int hi=1000;
            int mid = (lo+hi)/2;
            while(lo<hi)
            {
                if(customfunction.f(x,mid)==z){
                    res.push_back({x,mid});
                    break;
                }
                if(customfunction.f(x,mid)<z) lo=mid+1;
                else hi=mid;
                mid = (hi+lo)/2;
            }
        }
        return res;
        
    }
};