LeetCode 1237. 找出给定方程的正整数解

f(x, y) < f(x + 1, y)
f(x, y) < f(x, y + 1)

interface CustomFunction {
public:
  // Returns positive integer f(x, y) for any given positive integer x and y.
  int f(int x, int y);
};

示例 1：
输入：function_id = 1, z = 5
输出：[[1,4],[2,3],[3,2],[4,1]]
解释：function_id = 1 表示 f(x, y) = x + y

示例 2：
输入：function_id = 2, z = 5
输出：[[1,5],[5,1]]
解释：function_id = 2 表示 f(x, y) = x * y
 
提示：
1 <= function_id <= 9
1 <= z <= 100
题目保证 f(x, y) == z 的解处于 1 <= x, y <= 1000 的范围内。
在 1 <= x, y <= 1000 的前提下，题目保证 f(x, y) 是一个 32 位有符号整数。

class Solution {
public:
    vector<vector<int>> findSolution(CustomFunction& cf, int z) {
        int x = 1, y = 1000, val;
        vector<vector<int>> ans;
        while(x<=1000 && y >=1)
        {
        	val = cf.f(x,y);
        	if(val < z)
        		x++;
        	else if(val > z)
        		y--;
        	else
        	{
        		ans.push_back({x,y});
        		x++;
        	}
        }
        return ans;
    }
};

class Solution {
public:
    vector<vector<int>> findSolution(CustomFunction& cf, int z) {
        int x = 1000, y = 1, val;
        vector<vector<int>> ans;
        while(x>=1 && y<=1000)
        {
        	val = cf.f(x,y);
        	if(val < z)
        		y++;
        	else if(val > z)
        		x--;
        	else
        	{
        		ans.push_back({x,y});
        		x--;
        	}
        }
        return ans;
    }
};