# C++, Concise code

• ``````class Solution {
public:
bool judgePoint24(vector<int>& nums) {
sort(nums.begin(), nums.end());
do {
if (valid(nums)) return true;
} while(next_permutation(nums.begin(), nums.end()));
return false;
}
private:
bool valid(vector<int>& nums) {
double a = nums[0], b = nums[1], c = nums[2], d = nums[3];
if (valid(a+b, c, d) || valid(a-b, c, d) || valid(a*b, c, d) || valid(a/b, c, d)) return true;
if (valid(a, b+c, d) || valid(a, b-c, d) || valid(a, b*c, d) || valid(a, b/c, d)) return true;
if (valid(a, b, c+d) || valid(a, b, c-d) || valid(a, b, c*d) || valid(a, b, c/d)) return true;
return false;
}
bool valid(double a, double b, double c) {
if (valid(a+b, c) || valid(a-b, c) || valid(a*b, c) || b&&valid(a/b, c)) return true;
if (valid(a, b+c) || valid(a, b-c) || valid(a, b*c) || c&&valid(a, b/c)) return true;
return false;
}
bool valid(double a, double b) {
if (abs(a+b-24.0) < 0.0001 || abs(a-b-24.0) < 0.0001 || abs(a*b-24.0) < 0.0001 || b&&abs(a/b-24.0) < 0.0001)
return true;
return false;
}
};
``````

• @zestypanda said in C++, Concise code:

``````class Solution {
public:
bool judgePoint24(vector<int>& nums) {
sort(nums.begin(), nums.end());
do {
if (valid(nums)) return true;
} while(next_permutation(nums.begin(), nums.end()));
return false;
}
private:
bool valid(vector<int>& nums) {
double a = nums[0], b = nums[1], c = nums[2], d = nums[3];
if (valid(a+b, c, d) || valid(a-b, c, d) || valid(a*b, c, d) || valid(a/b, c, d)) return true;
if (valid(a, b+c, d) || valid(a, b-c, d) || valid(a, b*c, d) || valid(a, b/c, d)) return true;
if (valid(a, b, c+d) || valid(a, b, c-d) || valid(a, b, c*d) || valid(a, b, c/d)) return true;
return false;
}
bool valid(double a, double b, double c) {
if (valid(a+b, c) || valid(a-b, c) || valid(a*b, c) || b&&valid(a/b, c)) return true;
if (valid(a, b+c) || valid(a, b-c) || valid(a, b*c) || c&&valid(a, b/c)) return true;
return false;
}
bool valid(double a, double b) {
if (abs(a+b-24.0) < 0.0001 || abs(a-b-24.0) < 0.0001 || abs(a*b-24.0) < 0.0001 || b&&abs(a/b-24.0) < 0.0001)
return true;
return false;
}
};
``````
``````    if (abs(a+b-24.0) < 0.0001 || abs(a-b-24.0) < 0.0001 || abs(a*b-24.0) < 0.0001 || b&&abs(a/b-24.0) < 0.0001)
``````

In the above code, could you explain what's special about checking that abs(a+b-24.0) is less than 0.0001? Why not 0.000000001 or some other close to 0 value. Does 4 decimal places have some special meaning that's suffices for this problem?

• @zestypanda said in C++, Concise code:

next_permutation

Nice solution.

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