Application of stack -- bracket matching problem

Application of stack -- bracket matching problem

1, Problem introduction:

2, Algorithm idea:

There are four cases of bracket matching:

• The pairing order of left and right brackets is incorrect
• Left bracket is more than right bracket
• Right bracket is more than left bracket
• Left and right brackets match successfully
  Specific implementation method: sequence scan arithmetic expression (expressed as a string), when three types of left parentheses are encountered, let the parentheses stack. When a certain type of right bracket is scanned, compare whether the top bracket of the current stack matches it. If it matches, Backstack will continue to judge: if the top symbol of the current stack is different from the currently scanned bracket, the matching order of the left and right brackets is incorrect. If the string is currently a certain type of right bracket and the stack is empty, then the right bracket is more than the left bracket; if the stack is not empty at the end of the string cycle scanning (that is, there is a certain type of left bracket in the stack), then the left bracket is more than the right bracket; if the above three situations do not occur, then the left bracket matches correctly.

3, Code implementation (Visual Studio 2017 development environment)

Header file stack.h

#pragma once #include<windows.h> typedef struct Stacknode { Elemtype data; struct Stacknode *next; }Stacktype; //initialization void InitStack(Stacktype **top) { *top = (Stacktype *)malloc(sizeof(Stacktype)); (*top)->next = NULL; } //Push operation int pushStack(Stacktype *top, Elemtype x) { Stacktype *p; p = (Stacktype*)malloc(sizeof(Stacktype));//Application node p->data = x; p->next = top->next; top->next = p; return true; } //Stack out operation Elemtype popStack(Stacktype *top) { Stacktype *p; Elemtype x; if (top->next == NULL) { printf("Empty stack!!"); return NULL; } else { p = top->next; top->next = p->next; x = p->data; free(p); return x; } } //Data element at the top of stack Elemtype GetTop(Stacktype *top, Elemtype *x) { if (top->next == NULL) { return NULL; } else { *x = top->next->data; return (top->next->data); } } //Judge stack is not empty int StackNotEmpty(Stacktype *top) { if (top->next != NULL) { return 1; } else { return 0; } } //parenthesis matching void bracket(char exp[], int n) { //Determine whether the left and right parentheses of the string exp with n characters are matched correctly Stacktype *myStack; int i; char c; InitStack(&myStack);//Initial Stack for (i = 0; i < n; i++) { if ((exp[i] == '(') || (exp[i] == '[') || (exp[i] == '{')) {//Left parenthesis encountered, stack pushStack(myStack, exp[i]); } else if ((exp[i] == ')') && StackNotEmpty(myStack) && GetTop(myStack, &c) && c == '(') {//Judgment '()' popStack(myStack); } else if ((exp[i] == ')') && StackNotEmpty(myStack) && GetTop(myStack, &c) && c != '(') { printf("The pairing order of left and right brackets is incorrect!\n"); return; } else if ((exp[i] == ']') && StackNotEmpty(myStack) && GetTop(myStack, &c) && c == '[') {//Judgment '[]' popStack(myStack); } else if ((exp[i] == ']') && StackNotEmpty(myStack) && GetTop(myStack, &c) && c != '[') { printf("The pairing order of left and right brackets is incorrect!\n"); return; } else if ((exp[i] == '}') && StackNotEmpty(myStack) && GetTop(myStack, &c) && c == '{') {//Judge '{}' popStack(myStack); } else if ((exp[i] == '}') && StackNotEmpty(myStack) && GetTop(myStack, &c) && c != '{') { printf("The pairing order of left and right brackets is incorrect!\n"); return; } else if ((exp[i] == ')') || (exp[i] == ']') || (exp[i] == '}') && !StackNotEmpty(myStack)) { printf("Right bracket is more than left bracket!\n"); return; } } if (StackNotEmpty(myStack)) {//When the character array traverses, the stack is not empty, then the left bracket is more than the right bracket printf("Left bracket is more than right bracket!\n"); return; } else { printf("**Left and right brackets match successfully**\n"); } }

Source file:

#include<stdio.h> #include<malloc.h> #include<stdlib.h> typedef char Elemtype; #include"stack.h" int main() { int n;//Character array size printf("Please enter the character array size\n"); scanf("%d",&n); char *a; a = (char *)calloc(n, sizeof(char));//Request n spaces of char type for dynamic array getchar(); printf("Please enter the contents of character array\n"); for (int i = 0; i < n; i++) { scanf("%c", &a[i]); } printf("\n"); bracket(a,n); system("pause"); return 0; }

4, Test results