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, 0, 0);
        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 + 1; i < 10; ++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 == 1) return ret;
    if (num < 7 && num > 1) {
        ret.push_back('a' + (num - 2) * 3);
        ret.push_back('a' + (num - 2) * 3 + 1);
        ret.push_back('a' + (num - 2) * 3 + 2);
    } else if (num == 7) {
        ret.push_back('p');
        ret.push_back('p' + 1);
        ret.push_back('p' + 2);
        ret.push_back('p' + 3);
    } else if (num == 8) {
        ret.push_back('t');
        ret.push_back('t' + 1);
        ret.push_back('t' + 2);
    } else if (num == 9) {
        ret.push_back('w');
        ret.push_back('w' + 1);
        ret.push_back('w' + 2);
        ret.push_back('w' + 3);
    }
    return ret;
}

void dfs(string& s, int t, string &d) {
    if (t == d.size() && s.size() > 0) {
        ret.push_back(s);
        return;
    }
    vector<char> cs = getChar(d[t] - '0');
    for (int i = 0; i < cs.size(); ++i) {
        s.push_back(cs[i]);
        dfs(s, t + 1, d);
        s.pop_back();
    }
}

vector<string> letterCombinations(string& digits) {
    // Write your code here
    string s = "";
    dfs(s, 0, digits);
    return ret;
}
};