leetcode 46-Permutations and 47-Permutations II

Permutations

Given a collection of numbers, return all possible permutations.

For example,

[1,2,3]

have the following permutations:

[1,2,3]

,

[1,3,2]

,

[2,1,3]

,

[2,3,1]

,

[3,1,2]

,
and

[3,2,1]

.

Permutations II

Given a collection of numbers that might contain duplicates, return all possible unique permutations.

For example,

[1,1,2]

have the following unique permutations:

[1,1,2]

,

[1,2,1]

,
and

[2,1,1]

.

全排列问题
第二个题目基于第一题。第二题给的数组中还有可能相等的元素。

请參照 全 排 列

题一代码

class Solution {
public:
vector<vector<int>> permute(vector<int>& nums) {
vector<vector<int>>v;
v.clear();
vector<int>a;
next_c(v,nums.size(),a,nums,0);
return v;
}
void next_c(vector<vector<int>>&v,int n,vector<int>& a,vector<int>& b,int cur) /// b[]中的数能够同样
{
if(cur==n){
v.push_back(a);
}
else{
for(int i=0;i<n;i++)
if(!i||b[i]!=b[i-1])///
{
int c1=0,c2=0;
for(int j=0;j<cur;j++) if(a[j]==b[i]) c1++;
for(int j=0;j<n;j++) if(b[j]==b[i]) c2++;
if(c1<c2){
a.push_back(b[i]);// 不能用a[cur]=b[i];
next_c(v,n,a,b,cur+1);
a.pop_back();
}
}
}
}
};

题二代码。当然能够过题一。

class Solution {
public:
vector<vector<int>>v;
vector<vector<int>> permuteUnique(vector<int>& nums) {
v.clear();
vector<int>a;a.clear();
sort(nums.begin(),nums.end());
next_c(nums.size(),a,nums,0);
return v;
}
void next_c(int n,vector<int>& a,vector<int>& b,int cur) /// b[]中的数能够同样
{
if(cur==n){
v.push_back(a);
}
else{
for(int i=0;i<n;i++)
if(!i||b[i]!=b[i-1])///
{
int c1=0,c2=0;
for(int j=0;j<cur;j++) if(a[j]==b[i]) c1++;
for(int j=0;j<n;j++) if(b[j]==b[i]) c2++;
if(c1<c2){
a.push_back(b[i]); //a[cur]=b[i];
next_c(n,a,b,cur+1);
a.pop_back();
}
}
}
}
};