2025-05-17提交

20.valid-parentheses.java

@@ -0,0 +1,78 @@
+/*
+ * @lc app=leetcode id=20 lang=java
+ *
+ * [20] Valid Parentheses
+ */
+
+// @lc code=start
+
+import java.util.Deque;
+
+class Solution {
+    public boolean isValid(String s) {
+        int br_1_cnt = 0, br_2_cnt = 0, br_3_cnt = 0;
+        Deque<Integer> op_type_stack = new ArrayDeque<Integer>();
+        for(int i=0;i<s.length();i++) {
+            char ch = s.charAt(i);
+            if(isOpenBr(ch)) {
+                int op_type = getOpenBrType(ch);
+                op_type_stack.push(op_type);
+                if(op_type == 1) {
+                    br_1_cnt++;
+                } else if(op_type == 2) {
+                    br_2_cnt++;
+                } else if(op_type == 3) {
+                    br_3_cnt++;
+                }
+            } else {
+                int close_type = getCloseBrType(ch);
+                if(op_type_stack.isEmpty()) {
+                    return false;
+                } else if(op_type_stack.peek() != close_type) {
+                    return false;
+                }
+                op_type_stack.pop();
+                if(close_type == 1) {
+                    br_1_cnt--;
+                } else if(close_type == 2) {
+                    br_2_cnt--;
+                } else if(close_type == 3) {
+                    br_3_cnt--;
+                }
+            }
+        }
+        return br_1_cnt == 0 && br_2_cnt == 0 && br_3_cnt == 0;
+    }
+
+    private boolean isOpenBr(char ch) {
+        return ch == '(' || ch == '[' || ch == '{';
+    }
+
+    private int getOpenBrType(char ch) {
+        switch(ch) {
+            case '(':
+                return 1;
+            case '[':
+                return 2;
+            case '{':
+                return 3;
+            default:
+                throw new RuntimeException("invalid open brack");
+        }
+    }
+
+    private int getCloseBrType(char ch) {
+        switch(ch) {
+            case ')':
+                return 1;
+            case ']':
+                return 2;
+            case '}':
+                return 3;
+            default:
+                throw new RuntimeException("invalid close brack");
+        }
+    }
+}
+// @lc code=end
+