目录

39 组合总和

40 组合总和II

131分割回文串

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39 组合总和

class Solution {
    List<List<Integer>>res = new ArrayList<>();
    List<Integer>newList = new LinkedList<>();
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        dfs(candidates,target,0);
        return res;
    }
    private void dfs(int candidates[],int target,int cnt){
        if(target < 0)return;
        if(target == 0){
            res.add(new ArrayList(newList));
            return;
        }
        for(int i = cnt;i < candidates.length;i++){
            target -= candidates[i];
            newList.add(candidates[i]);
            dfs(candidates,target,i);
            target += candidates[i];
            newList.remove(newList.size() - 1);
        }
    }
}

时间复杂度O(n×)n为数组长度

空间复杂度O(target)最差情况下为targrt 

40 组合总和II

class Solution {
    List<List<Integer>>res = new ArrayList<>();
    List<Integer>path = new LinkedList<>();
    boolean st[];
    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
        Arrays.sort(candidates);
        st = new boolean[candidates.length];
        Arrays.fill(st,false);
        dfs(candidates,target,0);
        return res;
    }
    private void dfs(int candidates[],int target,int cnt){
        if(target < 0)return;
        if(target == 0){
            res.add(new LinkedList(path));
            return;
        }
        for(int i = cnt;i < candidates.length;i++){
            if(i > 0 && candidates[i] == candidates[i - 1] && !st[i - 1])continue;
            target -= candidates[i];
            path.add(candidates[i]);
            st[i] = true;
            dfs(candidates,target,i + 1);
            path.remove(path.size() - 1);
            st[i] = false;
            target += candidates[i];
        }
    }
}

时间复杂度O(n×)n为数组长度

空间复杂度O(n)最差情况下为n

131分割回文串