91 lines
2.9 KiB
C
91 lines
2.9 KiB
C
// 中序线索二叉树构建（根为1）
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// 输入：n，随后 n 行，每行两个整数 l、r（0 表示无孩子）。
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// 输出：n 行，每行四个整数：lchild(i) ltag(i) rchild(i) rtag(i)
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// 规则：
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// - 若有左儿子：ltag(i)=0，lchild(i) 为左儿子编号；否则 ltag(i)=1，lchild(i) 为中序前驱，无前驱为 -2。
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// - 若有右儿子：rtag(i)=0，rchild(i) 为右儿子编号；否则 rtag(i)=1，rchild(i) 为中序后继，无后继为 -1。
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#include <stdio.h>
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#include <stdlib.h>
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int main(void) {
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int n;
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if (scanf("%d", &n) != 1) return 0;
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if (n <= 0) return 0;
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int *L = (int *)malloc((n + 1) * sizeof(int));
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int *R = (int *)malloc((n + 1) * sizeof(int));
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if (!L || !R) return 0;
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for (int i = 1; i <= n; ++i) {
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int l, r;
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if (scanf("%d %d", &l, &r) != 2) {
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free(L); free(R);
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return 0;
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}
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L[i] = l; R[i] = r;
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}
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// 迭代中序遍历，生成访问序列 order
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int *stack = (int *)malloc((n + 1) * sizeof(int));
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int *order = (int *)malloc(n * sizeof(int));
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if (!stack || !order) { free(L); free(R); return 0; }
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int top = 0, k = 0;
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int cur = 1; // 根为 1
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while (cur || top) {
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if (cur) {
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stack[top++] = cur;
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cur = L[cur];
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} else {
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int u = stack[--top];
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order[k++] = u;
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cur = R[u];
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}
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}
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// 位置映射：pos[node] = 在中序序列中的索引
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int *pos = (int *)malloc((n + 1) * sizeof(int));
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if (!pos) { free(stack); free(order); free(L); free(R); return 0; }
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for (int i = 1; i <= n; ++i) pos[i] = -1;
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for (int i = 0; i < k; ++i) pos[order[i]] = i;
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// 输出域与标记域
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int *outL = (int *)malloc((n + 1) * sizeof(int));
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int *ltag = (int *)malloc((n + 1) * sizeof(int));
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int *outR = (int *)malloc((n + 1) * sizeof(int));
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int *rtag = (int *)malloc((n + 1) * sizeof(int));
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if (!outL || !ltag || !outR || !rtag) {
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free(pos); free(stack); free(order); free(L); free(R);
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return 0;
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}
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for (int i = 1; i <= n; ++i) {
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if (L[i]) { // 有左儿子
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ltag[i] = 0;
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outL[i] = L[i];
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} else { // 无左儿子，线索到中序前驱
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ltag[i] = 1;
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if (pos[i] > 0) outL[i] = order[pos[i] - 1];
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else outL[i] = -2; // 无前驱
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}
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if (R[i]) { // 有右儿子
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rtag[i] = 0;
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outR[i] = R[i];
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} else { // 无右儿子，线索到中序后继
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rtag[i] = 1;
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if (pos[i] >= 0 && pos[i] < k - 1) outR[i] = order[pos[i] + 1];
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else outR[i] = -1; // 无后继
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}
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}
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for (int i = 1; i <= n; ++i) {
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printf("%d %d %d %d\n", outL[i], ltag[i], outR[i], rtag[i]);
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}
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free(outL); free(ltag); free(outR); free(rtag);
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free(pos); free(stack); free(order);
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free(L); free(R);
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return 0;
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} |