数据N个元素的和的组合

目录

/*
写一个函数 void foo(arr, m, n)，arr是整数数组，m是个数，n是和，打印所有和为n的
二维数组，注意兼顾性能。 例子： arr 为[-1，1，2，3，4，5，6] m=2, n=5时，打印 [
[1，4]，[2，3]，[-1，6] ] m=3, n=6时，打印[ [-1，1，6], [-1,2,5], [-1,3,4],
[1,2,3] ]
 */
#include <iostream>
#include <vector>
using namespace std;

void print(vector<vector<int>> group) {
  cout << "[";
  for (auto &pair : group) {
    cout << "[";
    for (auto &item : pair) {
      cout << item << " ";
    }
    cout << "\b], ";
  }
  cout << "\b\b]" << endl;
}

vector<vector<int>> TwoNumSum(int arr[], size_t len, int argSum) {
  int i = 0, j = int(len) - 1;
  int sum = 0;
  vector<vector<int>> ret;
  while (i < j) {
    sum = arr[i] + arr[j];
    if (sum == argSum) {
      vector<int> group;
      group.push_back(arr[i]);
      group.push_back(arr[j]);
      ret.push_back(group);
      i++;
    } else if (sum < argSum) {
      i++;
    } else {
      j--;
    }
  }
  return ret;
}

int TwoNumSum(int arr[], size_t len, int argSum, vector<vector<int>> &ret) {

  int add = ret.size();
  int i = 0, j = int(len) - 1;
  int sum = 0;
  while (i < j) {
    sum = arr[i] + arr[j];
    if (sum == argSum) {
      vector<int> group;
      group.push_back(arr[i]);
      group.push_back(arr[j]);
      ret.push_back(group);
      i++;
    } else if (sum < argSum) {
      i++;
    } else {
      j--;
    }
  }
  return ret.size() - add;
}

int NNumSum(int arr[], int arrLen, int num, int argSum,
            vector<vector<int>> &result) {
  int add = result.size();
  if (num == 2) {
    return TwoNumSum(arr, arrLen, argSum, result);
  } else {
    for (int i = 0; i < arrLen - num; i++) {
      int addNum = NNumSum(&arr[i + 1], arrLen - i - 1, num - 1,
                           argSum - arr[i], result);

      if (addNum) {
        vector<vector<int>>::iterator iter = result.end() - addNum;
        for (; iter != result.end(); iter++) {
          iter->push_back(arr[i]);
        }
      }
    }
  }
  return result.size() - add;
}

int main() {
  int arr[] = {-1, 1, 2, 3, 4, 5, 6};
  print(TwoNumSum(arr, int(sizeof(arr) / sizeof(int)), 5));
  vector<vector<int>> ret;
  NNumSum(arr, int(sizeof(arr) / sizeof(int)), 3, 6, ret);
  print(ret);
  return 0;
}