[英]Finding Minimum Key and Predecessor in B-Tree
说明如何找到存储在B树中的最小密钥,以及如何找到存储在B树中的给定密钥的前身。
To Find Minimum Key 查找最小密钥
To find the predecessor 寻找前辈
Then there are two cases 然后有两种情况
If that element have left children, find the largest in that sub-tree rooted at that left children 如果该元素具有左子元素,请在以该左子元素为根的子树中找到最大的子元素
If that element haven't left children, you have to go upward 如果该要素还没有留下孩子,那么您必须向上
You can write recursive function to traverse a B-tree (from the root) via left and right nodes of each parent node. 您可以编写递归函数,以通过每个父节点的左右节点遍历B树(从根开始)。 During this you can compare all values and find minimum and its parent node. 在此期间,您可以比较所有值并找到最小值及其父节点。
#define BT_T 3// degree of B-tree
#define INF -32768
//struct of a node of B-tree
struct bnode {
int num;//number of keys in a bnode
int leaf; //1 for leaf,0 for not leaf
int value[2*BT_T -1]; //suppose all the key in B-tree is positive.
struct bnode *child[2*BT_T];
};
//minimum is the most left leaf's first value.
int find_min(struct bnode *p) {
if(p==NULL)
return -1;
if(!p->leaf)
find_min(p->child[0]);
else
return p->value[0];
}
//a predecessor's candidate of a given key are less than the key.
//the predecessor among the candidate is the largest one of them.
int find_predecessor(struct bnode *node,int val) {
int i,temp,max = INF;
for(i=0;i<num-1;i++) {
if(node->value[i] >= val)
break;
if(max > node->value[i]) {
max = ->value[i];
temp = find_predecessor(node->child[i],val);
max = (temp>max?temp:max);
}
}
return max;
//when there is no predecess,max is INF.
}
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