leetcode solutions

#104

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxDepth(TreeNode root) {
        
        int left = 0;
        int right = 0;
        
        if (root == null) {
            return 0;
        }
        
        if (root.left == null && root.right == null) {
            return 1;
        }
        
        if (root.left != null) {
            left = this.maxDepth(root.left);
        }
        
        if (root.right != null) {
            right = this.maxDepth(root.right);
        }
        
        return 1 + (left > right ? left : right);
        
    }
}

#171

public class Solution {
    public int titleToNumber(String s) {
        int result = 0;
        for (int i = 0, len = s.length(); i < len; i++) {
            result *= 26;
            result += s.charAt(i) - 'A' + 1;
        }
        return result;
    }
}

#20

class Solution {
public:
    bool isValid(string s) {
        stack<char> stk;
        for (string::iterator i = s.begin(); i != s.end(); ++i) {
            switch (*i) {
                case 40:
                    stk.push(41);
                    break;
                case 123:
                    stk.push(125);
                    break;
                case 91:
                    stk.push(93);
                    break;
                case 41: case 125: case 93:

                    if (stk.empty()) {
                        return false;
                    }

                    int top = stk.top();
                    if (top != *i) {
                        return false;
                    }
                    stk.pop();
                }
        }
        return stk.empty();
    }
};

#88

class Solution {
public:
    void merge(int A[], int m, int B[], int n) {
        
        
        if (m > 0 && n == 0) {
            return;
        }
        
        if (m == 0 && n > 0) {
            while (n >= 0) {
                A[--n] = B[n];
            }
            return;
        }
        
        int total = m + n;
        int tmp[total];
        
        for (int i = 0, j = 0; i + j < total;) {
            
            if (i == m) {
                tmp[i + j] = B[j++];
                continue;
            }
            
            if (j == n) {
                tmp[i + j] = A[i++];
                continue;
            }
            
            if (A[i] < B[j]) {
                tmp[i + j] = A[i++];
            }
            else {
                tmp[i + j] = B[j++];
            }
        }
        
        for (int i = 0; i < total; i++) {
            A[i] = tmp[i];
        }
        
    }
};