46, 47:Permutations 1, 2

46. Permutations

class Solution {
public:
    void DFS(int k, int& n, int* vis, vector<int>& nums, vector<int>& chs, vector<vector<int>>& result){
        if(n == k){
            result.push_back(chs);
            return;
        }
        for(int i = 0; i < n; i++){
            if(vis[i]) continue;
            vis[i] = 1; chs.push_back(nums[i]);
            DFS(k+1, n, vis, nums, chs, result);
            vis[i] = 0; chs.pop_back();
        }
    }

    vector<vector<int>> permute(vector<int>& nums) {
        int n = nums.size();
        int vis[n] = {0};
        vector<int> chs;
        vector<vector<int>> result;
        DFS(0, n, vis, nums, chs, result);
        return result;
    }
};

47. Permutations II

和Combination Sum II是类似的，只用递归重复数字的第一个数字，后面都是重复的解。

class Solution {
public:
    void DFS(int k, int& n, int* vis, vector<int>& nums, vector<int>& chs, vector<vector<int>>& result){
        if(n == k){
            result.push_back(chs);
            return;
        }
        for(int i = 0; i < n; i++){
            if(vis[i]) continue;
            if(i && nums[i] == nums[i-1] && !vis[i-1]) continue;
            vis[i] = 1; chs.push_back(nums[i]);
            DFS(k+1, n, vis, nums, chs, result);
            vis[i] = 0; chs.pop_back();
        }
    }

    vector<vector<int>> permuteUnique(vector<int>& nums) {
        int n = nums.size();
        int vis[n] = {0};
        vector<int> chs;
        vector<vector<int>> result;
        sort(nums.begin(), nums.end());
        DFS(0, n, vis, nums, chs, result);
        return result;
    }
};