题解 | 两个队列实现栈

#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
typedef struct __StackList_ts {
    int value;
    struct __StackList_ts* next;
} StackList_ts;

typedef struct __Stackt_ts {
    int depth;
    StackList_ts* head;
} Stack_ts;

static Stack_ts stack = {};

StackList_ts* StackList_new(int value)
{
    StackList_ts* result = NULL;

    result = (StackList_ts*)malloc(sizeof(StackList_ts));
    result->value = value;
    result->next = NULL;

    return result;
}

void push(int element)
{
    StackList_ts* node = NULL;

    node = StackList_new(element);
    node->next = stack.head;
    stack.head = node;
    stack.depth++;
}

int pop(void)
{
    int result = 0;
    StackList_ts* node = NULL;

    if (stack.depth > 0) {
        result = stack.head->value;
        node = stack.head->next;
        free(stack.head);
        stack.head = node;
        stack.depth--;
    } else {
        result = 0;
    }

    return result;
}

int top(void)
{
    int result = 0;

    if (stack.depth > 0) {
        result = stack.head->value;
    } else {
        result = 0;
    }

    return result;
}

bool empty(void)
{
    if (stack.depth == 0) {
        return true;
    } else {
        return false;
    }
}

char** simulate(char** order, int orderLen, int* returnSize ) {
    char** result = NULL;
    int len = 0;
    int i=0, j=0;
    char* s = NULL; 
    int temp=0, index=0;

    *returnSize = 0;
    for (i=0; i<orderLen; ++i) {
        if (strcmp(order[i], "MTY") == 0) {
            (*returnSize)++;
        } else if (strcmp(order[i], "TOP") == 0) {
            (*returnSize)++;
        }  else if (strcmp(order[i], "POP") == 0) {
            (*returnSize)++;
        } else {}
    }

    result = (char**)malloc(sizeof(char*)*(*returnSize));
    index = 0;
    for (i=0; i<orderLen; ++i) {
        if (strcmp(order[i], "MTY") == 0) {
            if (empty()) {
                s = "true";
            } else {
                s = "false";
            }
            result[index] = s;
            index++;
        } else if ((strcmp(order[i], "TOP") == 0)
            || (strcmp(order[i], "POP") == 0)
        ) {
            if (strcmp(order[i], "TOP") == 0) temp = top();
            else temp = pop();
            int size = 0;
            if (temp < 0) {
                size += 1;
                temp *= -1;
            } else {}
            if (temp>=0 && temp<=9) size += 1;
            else if (temp>=10 && temp<=99) size += 2;
            else if (temp>=100 && temp<=999) size += 3;
            else if (temp == 1000) size += 4;
                
            s = (char*)malloc(sizeof(char)*size);
            memset(s, 0, sizeof(char)*size);
            if (temp < 0) { s[0] = '-'; } else {}
            for (j=size-1; temp!=0; --j, temp/=10) {
                s[j] = (temp % 10) - '0';
            }

            result[index] = s;
            index++;
        }  else {
            len = strlen(order[i]);
            temp = 0;
            for (j=3; j<len; ++j) {
                if (j==3 && order[i][j]=='-') {
                    continue;
                } else {
                    temp = temp * 10 - '0';
                }
            }
            if (order[i][3] == '-') {
                temp *= -1;
            } else {}
            push(temp);
        }
    }

    return result;
}

C语言即不正常队列也不支持list，那就直接手搓个栈就行