min 为 O(1) 时间复杂度的栈

题目:

设计包含 min 函数的栈.

定义栈的数据结构, 要求添加一个 min 函数, 能够得到栈的最小元素.

要求函数 min, push, pop 时间复杂度都是 O(1).

 

思路:

为当前 min 值添加一个指向 前一个 min 位置的 地址偏移值 或指针.

 

实现: --- 添加偏移值

#include <stdio.h> #include <stdlib.h> #include <string.h> #define STACK_INIT_LEN 100 #define STACK_INC_LEN 100 #define STACK_EMPTY -9999 struct sta_unit { int value; int min_pre; }; struct stack { struct sta_unit *base; struct sta_unit *top; int size; int min; }; static char *menu[] = { "1 --- push one item./n", "2 --- pop one item./n", "3 --- get the min./n", "0 --- quit./n" "Your choice: ", NULL }; void Show_menu(); struct stack *BuildStack(); int Pop(struct stack *sta); void Push(struct stack *sta, int value); int Min(struct stack *sta); int main() { struct stack *sta = NULL; int choice; int value; sta = BuildStack(); Show_menu(); scanf("%d", &choice); while(1) { switch(choice) { case 1: printf("Input the value to push: "); scanf("%d", &value); Push(sta, value); break; case 2: value = Pop(sta); if(value == STACK_EMPTY){ printf("Empty stack./n"); break; } printf("The poped value is: %d/n", value); break; case 3: value = Min(sta); if(value == STACK_EMPTY) { printf("Empty stack./n"); exit(1); } printf("The min value is: %d/n", value); break; case 0: exit(0); default: printf("Error input./n"); break; } printf("/n"); Show_menu(); scanf("%d", &choice); } free(sta->base); free(sta); return 0; } void Show_menu() { char **p; p = menu; while(NULL != *p) { printf("%s", *p); *p ++; } } struct stack *BuildStack() { struct stack *sta = NULL; sta = (struct stack *)malloc(sizeof(struct stack)); sta->base = NULL; sta->top = NULL; sta->size = 0; sta->min = -1; sta->base = (struct sta_unit *)malloc(STACK_INIT_LEN * sizeof(struct sta_unit)); if(NULL == sta->base) { printf("memory allocation failed in BuildStack./n"); exit(1); } sta->top = sta->base; sta->size = STACK_INIT_LEN; memset(sta->base, '/0', STACK_INIT_LEN*(sizeof(struct sta_unit))); return sta; }/* BuildStack() */ void Push(struct stack *sta, int value) { if((sta->top - sta->base) >= sta->size) { sta->base = (struct sta_unit *)realloc(sta->base,(sta->size + STACK_INC_LEN)*sizeof(struct sta_unit)); if(NULL == sta->base) { printf("Memory realloc failed in Push()/n"); exit(1); } sta->top = sta->base + sta->size; sta->size = sta->size + STACK_INC_LEN; } sta->top->value = value; if(sta->min != -1) { if(value <= (sta->base + sta->min)->value) { sta->top->min_pre = sta->min; sta->min = sta->top - sta->base; } } else { sta->min = 0; sta->top->min_pre = -1; } sta->top ++ ; }/* Push() */ int Pop(struct stack *sta) { int value; if(sta->min != -1) { if(sta->min == (sta->top - sta->base) - 1) { sta->top --; sta->min = sta->top->min_pre; value = sta->top->value; } else { sta->top --; value = sta->top->value; } } else return STACK_EMPTY; return value; }/* Pop() */ int Min(struct stack *sta) { if(sta->min != -1) return (sta->base + sta->min)->value; else return STACK_EMPTY; }/* Min() */  

 

 实现 --- 添加指针

#include <stdio.h> #include <stdlib.h> #include <string.h> #define STACK_INIT_LEN 100 #define STACK_INC_LEN 100 #define STACK_EMPTY -9999 struct sta_unit { int value; struct sta_unit *min_pre; }; struct stack { struct sta_unit *base; struct sta_unit *top; int size; struct sta_unit *min; }; static char *menu[] = { "1 --- push one item./n", "2 --- pop one item./n", "3 --- get the min./n", "0 --- quit./n" "Your choice: ", NULL }; void Show_menu(); struct stack *BuildStack(); int Pop(struct stack *sta); void Push(struct stack *sta, int value); int Min(struct stack *sta); int main() { struct stack *sta = NULL; int choice; int value; sta = BuildStack(); Show_menu(); scanf("%d", &choice); while(1) { switch(choice) { case 1: printf("Input the value to push: "); scanf("%d", &value); Push(sta, value); break; case 2: value = Pop(sta); if(value == STACK_EMPTY){ printf("Empty stack./n"); break; } printf("The poped value is: %d/n", value); break; case 3: value = Min(sta); if(value == STACK_EMPTY){ printf("Empty stack./n"); break; } printf("The min value is: %d/n", value); break; case 0: exit(0); default: printf("Error input./n"); break; } printf("/n"); Show_menu(); scanf("%d", &choice); } free(sta->base); free(sta); return 0; } void Show_menu() { char **p; p = menu; while(NULL != *p) { printf("%s", *p); *p ++; } } struct stack *BuildStack() { struct stack *sta = NULL; sta = (struct stack *)malloc(sizeof(struct stack)); sta->base = NULL; sta->top = NULL; sta->size = 0; sta->min = NULL; sta->base = (struct sta_unit *)malloc(STACK_INIT_LEN * sizeof(struct sta_unit)); if(NULL == sta->base) { printf("memory allocation failed in BuildStack./n"); exit(1); } sta->top = sta->base; sta->size = STACK_INIT_LEN; memset(sta->base, '/0', STACK_INIT_LEN*(sizeof(struct sta_unit))); return sta; }/* BuildStack() */ void Push(struct stack *sta, int value) { if((sta->top - sta->base) >= sta->size) { sta->base = (struct sta_unit *)realloc(sta->base,(sta->size + STACK_INC_LEN)*sizeof(struct sta_unit)); if(NULL == sta->base) { printf("Memory realloc failed in Push()/n"); exit(1); } sta->top = sta->base + sta->size; sta->size = sta->size + STACK_INC_LEN; } sta->top->value = value; if(sta->min != NULL) { if(value <= sta->min->value) { sta->top->min_pre = sta->min; sta->min = sta->top; } } else { sta->min = sta->base; sta->top->min_pre = NULL; } sta->top ++ ; }/* Push() */ int Pop(struct stack *sta) { int value; if(sta->min != NULL) { if(sta->min == sta->top - 1) { sta->top --; sta->min = sta->top->min_pre; value = sta->top->value; } else { sta->top --; value = sta->top->value; } } else return STACK_EMPTY; return value; }/* Pop() */ int Min(struct stack *sta) { if(sta->min != NULL) return sta->min->value; else return STACK_EMPTY; }/* Min() */