leetcode 40. 组合总和 II

题目：40. 组合总和 II - 力扣（LeetCode）

dfs。注意各种剪枝即可。

bool myComp(vector<int>& a, vector<int>& b) {
    for (int i = 0; i < min(a.size(), b.size()); i++) {
        if (a[i] < b[i]) {
            return true;
        }
        if (a[i] > b[i]) {
            return false;
        }
    }
    return false;
}
class Solution {
public:
    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
        vector<vector<int>> ret;
        vector<int> c;
        int sum = 0;
        sort(candidates.begin(), candidates.end());
        for (int i = 0; i < candidates.size(); i++) {
            if (candidates[i] <= target) {
                if (i > target) {
                    if (candidates[i - target] == candidates[i]) {
                        continue;
                    }
                }
                c.push_back(candidates[i]);
                sum += candidates[i];
            }
        }
        sort(c.begin(), c.end());
        
        vector<int> arr;
        dfs(c, 0, target, sum, arr, ret);
        vector<vector<int>> ans;
        if (ret.size()) {
            sort(ret.begin(), ret.end(), myComp);
            ans.push_back(ret[0]);
            for (int i = 1; i < ret.size(); i++) {
                vector<int>& a = ret[i - 1];
                vector<int>& b = ret[i];
                if (!isEqual(a, b)) {
                    ans.push_back(b);
                }
            }
        }
        
        return ans;
    }
    void dfs(vector<int>& c, int idx, int target, int sum, vector<int>& arr, vector<vector<int>>& ret) {
        if (idx >= c.size() || target <= 0 || sum < target) {
            return;
        }
        if (target < c[idx]) {
            return;
        }
        if (target == c[idx]) {
            arr.push_back(c[idx]);
            if (ret.empty() || !isEqual(arr, ret[ret.size() - 1])) {
                ret.push_back(arr);
            }
            arr.pop_back();
            return;
        }
        dfs(c, idx + 1, target, sum - c[idx], arr, ret);
        arr.push_back(c[idx]);
        dfs(c, idx + 1, target - c[idx], sum - c[idx], arr, ret);
        arr.pop_back();
    }
    bool isEqual(vector<int>& a, vector<int>& b) {
        if (a.size() != b.size()) {
            return false;
        }
        for (int i = 0; i < a.size(); i++) {
            if (a[i] != b[i]) return false;
        }
        return true;
    }
};