docs: 添加仓库地址到README；chore: 整理实验分析；feat: Kruskal最小生成树与图存储结构

exercise/28.c

@@ -0,0 +1,84 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct {
+    int *data;
+    int *mins;
+    int top;     // index of next insertion in data
+    int mtop;    // index of next insertion in mins
+    int cap;     // capacity
+} MinStack;
+
+static void ms_init(MinStack *s, int cap) {
+    s->data = (int *)malloc(sizeof(int) * cap);
+    s->mins  = (int *)malloc(sizeof(int) * cap);
+    s->top = 0;
+    s->mtop = 0;
+    s->cap = cap;
+}
+
+static int ms_empty(const MinStack *s) { return s->top == 0; }
+
+static void ms_push(MinStack *s, int x) {
+    // Assume total pushes won't exceed cap per problem constraints
+    s->data[s->top++] = x;
+    if (s->mtop == 0 || x <= s->mins[s->mtop - 1]) {
+        s->mins[s->mtop++] = x;
+    }
+}
+
+static void ms_pop(MinStack *s) {
+    if (s->top == 0) return; // ignore if empty
+    int v = s->data[s->top - 1];
+    s->top--;
+    if (s->mtop > 0 && v == s->mins[s->mtop - 1]) {
+        s->mtop--;
+    }
+}
+
+static int ms_top(const MinStack *s) {
+    return s->data[s->top - 1];
+}
+
+static int ms_get_min(const MinStack *s) {
+    return s->mins[s->mtop - 1];
+}
+
+static void ms_free(MinStack *s) {
+    free(s->data);
+    free(s->mins);
+    s->data = s->mins = NULL;
+    s->top = s->mtop = s->cap = 0;
+}
+
+int main(void) {
+    int n;
+    if (scanf("%d", &n) != 1) return 0;
+    MinStack st;
+    ms_init(&st, n > 0 ? n : 1);
+
+    for (int i = 0; i < n; ++i) {
+        int t; 
+        if (scanf("%d", &t) != 1) t = 0;
+        if (t == 1) {
+            int x; 
+            scanf("%d", &x);
+            ms_push(&st, x);
+        } else if (t == 2) {
+            ms_pop(&st);
+        } else if (t == 3) {
+            if (!ms_empty(&st)) {
+                printf("%d\n", ms_top(&st));
+            }
+        } else if (t == 4) {
+            if (!ms_empty(&st)) {
+                printf("%d\n", ms_get_min(&st));
+            }
+        } else {
+            // ignore unknown command
+        }
+    }
+
+    ms_free(&st);
+    return 0;
+}