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 -9999struct 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;}}elsereturn 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 -9999struct 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;}}elsereturn STACK_EMPTY;return value;}/* Pop() */int Min(struct stack *sta){if(sta->min != NULL)return sta->min->value;elsereturn STACK_EMPTY;}/* Min() */