🌗 367. 有效的完全平方数

难度: 🌗

• 问题描述
• 解法
• 输出

问题描述

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解法

class Solution {
    public boolean isPerfectSquare(int num) {
        // 思路:
        // 二分
        return mySol((long) num, 1, num);
    }

    private boolean mySol(long target, int left, int right) {
        // 递归终止条件
        if(left > right) {
            return false;
        }
        if(left == right) {
            if(target == (long) left * (long) right) {
                return true;
            } else {
                return false;
            }
        }
        // left < right
        int mid = left + ((right - left) >> 1);
        long mul = (long) mid * (long) mid;
        if(target == mul) {
            return true;
        } else if(target > mul) {
            left = mid + 1;
            return mySol(target, left, right);
        } else {
            // target < mul
            right = mid - 1;
            return mySol(target, left, right);
        }
    }
}

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输出