POJ 2255 Tree Recovery (二叉樹周遊)

#include <stdio.h>
#include <string.h>

char preOrder[27];
char inOrder[27];
int indexOfInOrderLetter[27];

void printPostOrderLetters(int preOrderStart, int preOrderEnd, int inOrderStart, int inOrderEnd){
	//直接求取先序周遊第一個字母即樹的根節點在後序周遊中的索引
	int rootIndexOfInOrderLetter = indexOfInOrderLetter[ preOrder[preOrderStart] - 'A'];
	
	int lenOfLeftTree = rootIndexOfInOrderLetter - inOrderStart;
	if (lenOfLeftTree > 0)
		printPostOrderLetters(preOrderStart + 1, preOrderStart + lenOfLeftTree, inOrderStart, rootIndexOfInOrderLetter - 1);
	
	int lenOfRightTree = inOrderEnd - rootIndexOfInOrderLetter;
	if (lenOfRightTree > 0)
		printPostOrderLetters(preOrderStart + lenOfLeftTree + 1, preOrderEnd, rootIndexOfInOrderLetter + 1, inOrderEnd);

	printf("%c", inOrder[rootIndexOfInOrderLetter]);

}

int main(){

	while (scanf("%s%s", preOrder, inOrder) != EOF){
		int i;
		for (i = 0; inOrder[i] != '\0'; i++)
			//技巧：記錄後序周遊的字母的索引
			indexOfInOrderLetter[ inOrder[i] - 'A' ] = i;

		int len = strlen(preOrder);

		printPostOrderLetters(0, len - 1, 0, len - 1);
		printf("\n");
	}

	return 0;
}