在 3 SUM问题中用了一个很蠢的暴力求解方法,之后报错显示无法分配内存,想必是对内存大小做了限制
terminate called after throwing an instance of ‘std::bad_alloc’ what(): std::bad_alloc
class Solution {
public:
vector<vector<int>> threeSum(vector<int>& nums) {
vector<vector<int>> res;
int i,j,k;
for(i=0;i<nums.size();i++){
for(j=i+1;j<nums.size();j++){
for(k=j+1;k<nums.size();k++)
if(nums[i]+nums[k]+nums[j]==0){
if(res.size()==0)
res.push_back({nums[i],nums[j],nums[k]});
else{
for(auto l:res)
if(find(l.begin(),l.end(),nums[i])==l.end() || find(l.begin(),l.end(),nums[j])==l.end() || find(l.begin(),l.end(),nums[k])==l.end())
res.push_back(nums[i],nums[j],nums[k]});
}
temp.clear();
}
}
}
return res;
}
};
于是更换思路,,优化原来的算法
1.给原来的排序
2.去重
public:
vector<vector<int>> threeSum(vector<int>& nums) {
vector<vector<int>> res;
sort(nums.begin(), nums.end());
for (int k = 0; k < nums.size(); ++k) {
if (nums[k] > 0) break;
if (k > 0 && nums[k] == nums[k – 1]) continue;
int target = 0 – nums[k];
int i = k + 1, j = nums.size() – 1;
while (i < j) {
if (nums[i] + nums[j] == target) {
res.push_back({nums[k], nums[i], nums[j]});
while (i < j && nums[i] == nums[i + 1]) ++i;
while (i < j && nums[j] == nums[j – 1]) –j;
++i; –j;
} else if (nums[i] + nums[j] < target) ++i;
else –j;
}
}
return res;
}
};