LEET code -- Valid Parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.


用stack就可以了
如果stack 的頭 不是相對應的左括弧 就是錯的

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bool isValid(char* s) { int size=256; char *stack=calloc(size,sizeof(char)); int stackHead=0; for(;*s;s++){ if(*s=='(' || *s=='{' || *s=='['){ stack[stackHead++]=*s; }else{ if(*s==')'){ if(stack[--stackHead]!='(')return false; }else if(*s=='}'){ if(stack[--stackHead]!='{')return false; }else if(*s==']'){ if(stack[--stackHead]!='[')return false; } } if (stackHead >= size*0.8){ stack=realloc(stack,sizeof(char)*size*2); size*=2; } } return stackHead==0? true:false; }