46. Permutations 全排列

Posted 2020-12-13 immiao0319

Given a collection of distinct integers, return all possible permutations.

Example:

Input: [1,2,3]
Output:
[
  [1,2,3],
  [1,3,2],
  [2,1,3],
  [2,3,1],
  [3,1,2],
  [3,2,1]
]

全排列是所有元素，所以index必须从0开始

class Solution {
    public List<List<Integer>> permute(int[] nums) {
    List<List<Integer>> list = new ArrayList<>();
    Arrays.sort(nums);
    backtrack(nums, new ArrayList<>(), list);
    return list;
}

private void backtrack(int [] nums, List<Integer> tempList, List<List<Integer>> list){
    if (tempList.size() == nums.length)
        list.add(new ArrayList<>(tempList));
    
        for(int i = 0; i < nums.length; i++){        
        if(tempList.contains(nums[i])) continue;
            
        tempList.add(nums[i]);
        backtrack(nums, tempList, list);
        tempList.remove(tempList.size() - 1);
    }
    
} 
}

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