Stay button --- 2020.3.10

543. Binary Tree diameter

class Solution {
    int max = 0;
    public int diameterOfBinaryTree(TreeNode root) {
            //遍历每一个节点,求出此节点作为根的树的深度,那么,左子树深度加右子树深度的最大值即是答案
            setDepth(root);
            return max;
    }

    public int setDepth(TreeNode root) {
        if (root != null) {
            int right = setDepth(root.right);
            int left = setDepth(root.left);
            if (right + left > max)
                max = right + left;
            return Math.max(right, left) + 1;
        }
        return 0;
    }
}

654. The largest binary tree

//递归+分治
class Solution {
    public TreeNode constructMaximumBinaryTree(int[] nums) {
        return construct(nums, 0, nums.length);
    }
    public TreeNode construct(int[] nums, int l, int r) {
        if (l == r)
            return null;
        int max_i = max(nums, l, r);
        TreeNode root = new TreeNode(nums[max_i]);
        root.left = construct(nums, l, max_i);
        root.right = construct(nums, max_i + 1, r);
        return root;
    }
    public int max(int[] nums, int l, int r) {
        int max_i = l;
        for (int i = l; i < r; i++) {
            if (nums[max_i] < nums[i])
                max_i = i;
        }
        return max_i;
    }
}

1221. segmentation balance string

//计数法
class Solution {
    public int balancedStringSplit(String s) {
        int num = 0;
        int n = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i)=='R')
                n++;
            if (s.charAt(i) == 'L')
                n--;
            if (n == 0)
                num++;
        }
        return num;
    }
}

//数组模拟栈
public int balancedStringSplit(String s) {

    int count = 0;
    int[] container = new int[s.length()];
    int size = 0;

    for (char c : s.toCharArray()) {
        if (size == 0 || c == container[size-1]) 
            container[size++] = c;              //放入容器
        else if (c != container[size-1]){
            size--;                             //匹配到了互异字母
            if (size == 0)
                count++;
        }
    }
    return count;
}

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