leetcode216-Combination Sum III

https://leetcode.com/problems/combination-sum-iii/

用dfs枚举。

class Solution {
public:
    int kk, nn;
    vector<vector<int>> res;
    vector<vector<int>> combinationSum3(int k, int n) {
        kk = k, nn = n;
        vector<int> r;
        dfs(r, , );
        return res;
    }

void dfs(vector<int> &a, int t, int sum) {
    if (a.size() >= kk || sum >= nn) {
        if (a.size() == kk && sum == nn) {
            res.push_back(a);
        }
        return;
    }
    for (int i = t + ; i < ; ++i) {
        a.push_back(i);
        dfs(a, i, sum + i);
        a.pop_back();
    }
}
};

其他同类题：

http://www.jiuzhang.com/solutions/search/?question=Combination+Sum

1.  http://www.lintcode.com/zh-cn/problem/letter-combinations-of-a-phone-number/

class Solution {
public:
    vector<string> ret;

vector<char> getChar(int num) {
    vector<char> ret;
    if (num == ) return ret;
    if (num <  && num > ) {
        ret.push_back('a' + (num - ) * );
        ret.push_back('a' + (num - ) *  + );
        ret.push_back('a' + (num - ) *  + );
    } else if (num == ) {
        ret.push_back('p');
        ret.push_back('p' + );
        ret.push_back('p' + );
        ret.push_back('p' + );
    } else if (num == ) {
        ret.push_back('t');
        ret.push_back('t' + );
        ret.push_back('t' + );
    } else if (num == ) {
        ret.push_back('w');
        ret.push_back('w' + );
        ret.push_back('w' + );
        ret.push_back('w' + );
    }
    return ret;
}

void dfs(string& s, int t, string &d) {
    if (t == d.size() && s.size() > ) {
        ret.push_back(s);
        return;
    }
    vector<char> cs = getChar(d[t] - '');
    for (int i = ; i < cs.size(); ++i) {
        s.push_back(cs[i]);
        dfs(s, t + , d);
        s.pop_back();
    }
}

vector<string> letterCombinations(string& digits) {
    // Write your code here
    string s = "";
    dfs(s, , digits);
    return ret;
}
};